mm: Page fault enhancements

PATCH Superseded Peter Xu 1 participant 19 messages Sep 26, 2019 – Oct 14, 2019

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Peter Xu

author reviewer

2019-09-26 09:39 UTC #0 lore raw

v5 cover mm: Page fault enhancements

This is v5 of the series. As Matthew suggested, I split the previous patch "mm: Return faster for non-fatal signals in user mode faults" into a few smaller ones:

1. One patch to introduce fatal_signal_pending(), and use it in archs that can directly apply

2. A few more patches to let the rest archs to use the new helper. With that we can have an unified entry for signal detection

3. One last patch to change fatal_signal_pending() to detect userspace non-fatal signal

Nothing should have changed in the rest patches. Because the fault retry patches will depend on the previous ones, I decided to simply repost all the patches.

Here's the new patchset layout:

Patch 1-2: cleanup, and potential bugfix of hugetlbfs on fault retry

Patch 3-9: let page fault to respond to non-fatal signals faster

Patch 10: remove the userfaultfd NOPAGE emulation

Patch 11-14: allow page fault to retry more than once

Patch 15-16: let gup code to use FAULT_FLAG_KILLABLE too

I would really appreciate any review comments for the series, especially for the first two patches which IMHO are even not related to this patchset and they should either cleanup or fix things.

Smoke tested on x86 only.

Thanks,

v5:
- split "mm: Return faster for non-fatal signals in user mode faults" into a few more patches, let all archs to use an unified entry for fast signal handling (fatal_signal_pending)

v4:
- use lore.kernel.org for all the links in commit messages [Kirill]
- one more patch ("mm/gup: Fix __get_user_pages() on fault retry of hugetlb") to fix hugetlb path on fault retry
- one more patch ("mm/gup: Allow to react to fatal signals") to:
- use down_read_killable() properly [Linus]
- pass in FAULT_FLAG_KILLABLE for all GUP [Linus]
- one more patch ("mm/userfaultfd: Honor FAULT_FLAG_KILLABLE in fault path") to let handle_userfaultfd() respect FAULT_FLAG_KILLABLE. Should have no functional change after previous two new patches.

v3:
- check fatal signals in __get_user_page_locked() [Linus]
- add r-bs

v2:
- resent previous version, rebase only

=============== v1 cover letter ==================

This series is split out of userfaultfd-wp series to only cover the general page fault changes, since it seems to make sense itself.

Basically it does two things:

(a) Allows the page fault handlers to be more interactive on not only SIGKILL, but also the rest of userspace signals (especially for user-mode faults), and,

(b) Allows the page fault retry (VM_FAULT_RETRY) to happen for more than once.

I'm keeping the CC list as in uffd-wp v5, hopefully I'm not sending too much spams...

And, instead of writting again the cover letter, I'm just copy-pasting my previous link here which has more details on why we do this:

https://patchwork.kernel.org/cover/10691991/

The major change from that latest version should be that we introduced a new page fault flag FAULT_FLAG_INTERRUPTIBLE as suggested by Linus
[1] to represents that we would like the fault handler to respond to non-fatal signals. Also, we're more careful now on when to do the immediate return of the page fault for such signals. For example, now we'll only check against signal_pending() for user-mode page faults and we keep the kernel-mode page fault patch untouched for it. More information can be found in separate patches.

The patchset is only lightly tested on x86.

All comments are greatly welcomed. Thanks,

[1] https://lkml.org/lkml/2019/6/25/1382

Peter Xu (16):
mm/gup: Rename "nonblocking" to "locked" where proper mm/gup: Fix __get_user_pages() on fault retry of hugetlb
mm: Introduce fault_signal_pending()
x86/mm: Use helper fault_signal_pending()
arc/mm: Use helper fault_signal_pending() arm64/mm: Use helper fault_signal_pending() powerpc/mm: Use helper fault_signal_pending() sh/mm: Use helper fault_signal_pending()
mm: Return faster for non-fatal signals in user mode faults
userfaultfd: Don't retake mmap_sem to emulate NOPAGE
mm: Introduce FAULT_FLAG_DEFAULT
mm: Introduce FAULT_FLAG_INTERRUPTIBLE
mm: Allow VM_FAULT_RETRY for multiple times mm/gup: Allow VM_FAULT_RETRY for multiple times mm/gup: Allow to react to fatal signals mm/userfaultfd: Honor FAULT_FLAG_KILLABLE in fault path

 arch/alpha/mm/fault.c           |  6 +--
 arch/arc/mm/fault.c             | 35 +++++--------
 arch/arm/mm/fault.c             |  7 +--
 arch/arm64/mm/fault.c           | 26 +++------
 arch/hexagon/mm/vm_fault.c      |  5 +-
 arch/ia64/mm/fault.c            |  5 +-
 arch/m68k/mm/fault.c            |  7 +--
 arch/microblaze/mm/fault.c      |  5 +-
 arch/mips/mm/fault.c            |  5 +-
 arch/nds32/mm/fault.c           |  5 +-
 arch/nios2/mm/fault.c           |  7 +--
 arch/openrisc/mm/fault.c        |  5 +-
 arch/parisc/mm/fault.c          |  8 ++-
 arch/powerpc/mm/fault.c         | 20 ++-----
 arch/riscv/mm/fault.c           |  9 +---
 arch/s390/mm/fault.c            | 10 ++--
 arch/sh/mm/fault.c              | 13 +++--
 arch/sparc/mm/fault_32.c        |  5 +-
 arch/sparc/mm/fault_64.c        |  5 +-
 arch/um/kernel/trap.c           |  3 +-
 arch/unicore32/mm/fault.c       |  8 ++-
 arch/x86/mm/fault.c             | 30 +++++------
 arch/xtensa/mm/fault.c          |  5 +-
 drivers/gpu/drm/ttm/ttm_bo_vm.c | 12 +++--
 fs/userfaultfd.c                | 62 ++++++++++------------
 include/linux/mm.h              | 81 ++++++++++++++++++++++++----
 include/linux/sched/signal.h    | 14 +++++
 mm/filemap.c                    |  2 +-
 mm/gup.c                        | 93 +++++++++++++++++++++------------
 mm/hugetlb.c                    | 17 +++---
 mm/shmem.c                      |  2 +-
 31 files changed, 279 insertions(+), 238 deletions(-)

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:39 UTC #1 lore raw

PATCH v5 1/16 mm/gup: Rename "nonblocking" to "locked" where proper

There's plenty of places around __get_user_pages() that has a parameter "nonblocking" which does not really mean that "it won't block" (because it can really block) but instead it shows whether the mmap_sem is released by up_read() during the page fault handling mostly when VM_FAULT_RETRY is returned.

We have the correct naming in e.g. get_user_pages_locked() or get_user_pages_remote() as "locked", however there're still many places that are using the "nonblocking" as name.

Renaming the places to "locked" where proper to better suite the functionality of the variable. While at it, fixing up some of the comments accordingly.

Reviewed-by Mike Rapoport <[email protected]>

Reviewed-by Jerome Glisse <[email protected]>

Reviewed-by David Hildenbrand <[email protected]>

Signed-off-by Peter Xu <[email protected]>

---
 mm/gup.c     | 44 +++++++++++++++++++++-----------------------
 mm/hugetlb.c |  8 ++++----
 2 files changed, 25 insertions(+), 27 deletions(-)

mm/gup.c +21 ~~-23~~

index 98f13ab37bac..eddbb95dcb8f 100644
@@ -622,12 +622,12 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
 }
 
 /*
- * mmap_sem must be held on entry.  If @nonblocking != NULL and
- * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
- * If it is, *@nonblocking will be set to 0 and -EBUSY returned.
+ * mmap_sem must be held on entry.  If @locked != NULL and *@flags
+ * does not include FOLL_NOWAIT, the mmap_sem may be released.  If it
+ * is, *@locked will be set to 0 and -EBUSY returned.
  */
 static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
-		unsigned long address, unsigned int *flags, int *nonblocking)
+		unsigned long address, unsigned int *flags, int *locked)
 {
 	unsigned int fault_flags = 0;
 	vm_fault_t ret;

@@ -639,7 +639,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 		fault_flags |= FAULT_FLAG_WRITE;
 	if (*flags & FOLL_REMOTE)
 		fault_flags |= FAULT_FLAG_REMOTE;
-	if (nonblocking)
+	if (locked)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;

@@ -665,8 +665,8 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	}
 
 	if (ret & VM_FAULT_RETRY) {
-		if (nonblocking && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
-			*nonblocking = 0;
+		if (locked && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
+			*locked = 0;
 		return -EBUSY;
 	}

@@ -743,7 +743,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
  *		only intends to ensure the pages are faulted in.
  * @vmas:	array of pointers to vmas corresponding to each page.
  *		Or NULL if the caller does not require them.
- * @nonblocking: whether waiting for disk IO or mmap_sem contention
+ * @locked:     whether we're still with the mmap_sem held
  *
  * Returns number of pages pinned. This may be fewer than the number
  * requested. If nr_pages is 0 or negative, returns 0. If no pages

@@ -772,13 +772,11 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
  * appropriate) must be called after the page is finished with, and
  * before put_page is called.
  *
- * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
- * or mmap_sem contention, and if waiting is needed to pin all pages,
- * *@nonblocking will be set to 0.  Further, if @gup_flags does not
- * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
- * this case.
+ * If @locked != NULL, *@locked will be set to 0 when mmap_sem is
+ * released by an up_read().  That can happen if @gup_flags does not
+ * have FOLL_NOWAIT.
  *
- * A caller using such a combination of @nonblocking and @gup_flags
+ * A caller using such a combination of @locked and @gup_flags
  * must therefore hold the mmap_sem for reading only, and recognize
  * when it's been released.  Otherwise, it must be held for either
  * reading or writing and will not be released.

@@ -790,7 +788,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		unsigned long start, unsigned long nr_pages,
 		unsigned int gup_flags, struct page **pages,
-		struct vm_area_struct **vmas, int *nonblocking)
+		struct vm_area_struct **vmas, int *locked)
 {
 	long ret = 0, i = 0;
 	struct vm_area_struct *vma = NULL;

@@ -834,7 +832,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 			if (is_vm_hugetlb_page(vma)) {
 				i = follow_hugetlb_page(mm, vma, pages, vmas,
 						&start, &nr_pages, i,
-						gup_flags, nonblocking);
+						gup_flags, locked);
 				continue;
 			}
 		}

@@ -852,7 +850,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		page = follow_page_mask(vma, start, foll_flags, &ctx);
 		if (!page) {
 			ret = faultin_page(tsk, vma, start, &foll_flags,
-					nonblocking);
+					   locked);
 			switch (ret) {
 			case 0:
 				goto retry;

@@ -1178,7 +1176,7 @@ EXPORT_SYMBOL(get_user_pages_remote);
  * @vma:   target vma
  * @start: start address
  * @end:   end address
- * @nonblocking:
+ * @locked: whether the mmap_sem is still held
  *
  * This takes care of mlocking the pages too if VM_LOCKED is set.
  *

@@ -1186,14 +1184,14 @@ EXPORT_SYMBOL(get_user_pages_remote);
  *
  * vma->vm_mm->mmap_sem must be held.
  *
- * If @nonblocking is NULL, it may be held for read or write and will
+ * If @locked is NULL, it may be held for read or write and will
  * be unperturbed.
  *
- * If @nonblocking is non-NULL, it must held for read only and may be
- * released.  If it's released, *@nonblocking will be set to 0.
+ * If @locked is non-NULL, it must held for read only and may be
+ * released.  If it's released, *@locked will be set to 0.
  */
 long populate_vma_page_range(struct vm_area_struct *vma,
-		unsigned long start, unsigned long end, int *nonblocking)
+		unsigned long start, unsigned long end, int *locked)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	unsigned long nr_pages = (end - start) / PAGE_SIZE;

@@ -1228,7 +1226,7 @@ long populate_vma_page_range(struct vm_area_struct *vma,
 	 * not result in a stack expansion that recurses back here.
 	 */
 	return __get_user_pages(current, mm, start, nr_pages, gup_flags,
-				NULL, NULL, nonblocking);
+				NULL, NULL, locked);
 }
 
 /*

mm/hugetlb.c +4 -4

index 6d7296dd11b8..31c2a6275023 100644
@@ -4270,7 +4270,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			 struct page **pages, struct vm_area_struct **vmas,
 			 unsigned long *position, unsigned long *nr_pages,
-			 long i, unsigned int flags, int *nonblocking)
+			 long i, unsigned int flags, int *locked)
 {
 	unsigned long pfn_offset;
 	unsigned long vaddr = *position;

@@ -4341,7 +4341,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				spin_unlock(ptl);
 			if (flags & FOLL_WRITE)
 				fault_flags |= FAULT_FLAG_WRITE;
-			if (nonblocking)
+			if (locked)
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 			if (flags & FOLL_NOWAIT)
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY |

@@ -4358,9 +4358,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				break;
 			}
 			if (ret & VM_FAULT_RETRY) {
-				if (nonblocking &&
+				if (locked &&
 				    !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
-					*nonblocking = 0;
+					*locked = 0;
 				*nr_pages = 0;
 				/*
 				 * VM_FAULT_RETRY must not return an

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:39 UTC #2 lore raw

PATCH v5 2/16 mm/gup: Fix __get_user_pages() on fault retry of hugetlb

In reply to Peter Xu

When follow_hugetlb_page() returns with *locked==0, it means we've got a VM_FAULT_RETRY within the fauling process and we've released the mmap_sem. When that happens, we should stop and bail out.

Signed-off-by Peter Xu <[email protected]>

---
 mm/gup.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

mm/gup.c +10 -0

index eddbb95dcb8f..e60d32f1674d 100644
@@ -833,6 +833,16 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 				i = follow_hugetlb_page(mm, vma, pages, vmas,
 						&start, &nr_pages, i,
 						gup_flags, locked);
+				if (locked && *locked == 0) {
+					/*
+					 * We've got a VM_FAULT_RETRY
+					 * and we've lost mmap_sem.
+					 * We must stop here.
+					 */
+					BUG_ON(gup_flags & FOLL_NOWAIT);
+					BUG_ON(ret != 0);
+					goto out;
+				}
 				continue;
 			}
 		}

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:39 UTC #3 lore raw

PATCH v5 3/16 mm: Introduce fault_signal_pending()

In reply to Peter Xu

For most architectures, we've got a quick path to detect fatal signal after a handle_mm_fault(). Introduce a helper for that quick path.

It cleans the current codes a bit so we don't need to duplicate the same check across archs. More importantly, this will be an unified place that we handle the signal immediately right after an interrupted page fault, so it'll be much easier for us if we want to change the behavior of handling signals later on for all the archs.

Note that currently only part of the archs are using this new helper, because some archs have their own way to handle signals. In the follow up patches, we'll try to apply this helper to all the rest of archs.

Another note is that the "regs" parameter in the new helper is not used yet. It'll be used very soon. Now we kept it in this patch only to avoid touching all the archs again in the follow up patches.

Signed-off-by Peter Xu <[email protected]>

---
 arch/alpha/mm/fault.c        |  2 +-
 arch/arm/mm/fault.c          |  2 +-
 arch/hexagon/mm/vm_fault.c   |  2 +-
 arch/ia64/mm/fault.c         |  2 +-
 arch/m68k/mm/fault.c         |  2 +-
 arch/microblaze/mm/fault.c   |  2 +-
 arch/mips/mm/fault.c         |  2 +-
 arch/nds32/mm/fault.c        |  2 +-
 arch/nios2/mm/fault.c        |  2 +-
 arch/openrisc/mm/fault.c     |  2 +-
 arch/parisc/mm/fault.c       |  2 +-
 arch/riscv/mm/fault.c        |  2 +-
 arch/s390/mm/fault.c         |  3 +--
 arch/sparc/mm/fault_32.c     |  2 +-
 arch/sparc/mm/fault_64.c     |  2 +-
 arch/unicore32/mm/fault.c    |  2 +-
 arch/xtensa/mm/fault.c       |  2 +-
 include/linux/sched/signal.h | 13 +++++++++++++
 18 files changed, 30 insertions(+), 18 deletions(-)

arch/alpha/mm/fault.c +1 -1

index 741e61ef9d3f..aea33b599037 100644
@@ -150,7 +150,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
 	   the fault.  */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/arm/mm/fault.c +1 -1

index 890eeaac3cbb..c8f2950fa733 100644
@@ -295,7 +295,7 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	 * signal first. We do not need to release the mmap_sem because
 	 * it would already be released in __lock_page_or_retry in
 	 * mm/filemap.c. */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
+	if (fault_signal_pending(fault, regs)) {
 		if (!user_mode(regs))
 			goto no_context;
 		return 0;

arch/hexagon/mm/vm_fault.c +1 -1

index b3bc71680ae4..d19beaf11b4c 100644
@@ -91,7 +91,7 @@ void do_page_fault(unsigned long address, long cause, struct pt_regs *regs)
 
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	/* The most common case -- we are done. */

arch/ia64/mm/fault.c +1 -1

index c2f299fe9e04..211b4f439384 100644
@@ -141,7 +141,7 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/m68k/mm/fault.c +1 -1

index e9b1d7585b43..a455e202691b 100644
@@ -138,7 +138,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 	fault = handle_mm_fault(vma, address, flags);
 	pr_debug("handle_mm_fault returns %x\n", fault);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return 0;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/microblaze/mm/fault.c +1 -1

index e6a810b0c7ad..cdde01dcdfc3 100644
@@ -217,7 +217,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/mips/mm/fault.c +1 -1

index f589aa8f47d9..31fda59199eb 100644
@@ -154,7 +154,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(regs))
 		return;
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

arch/nds32/mm/fault.c +1 -1

index 064ae5d2159d..c8f32b4784bd 100644
@@ -210,7 +210,7 @@ void do_page_fault(unsigned long entry, unsigned long addr,
 	 * signal first. We do not need to release the mmap_sem because it
 	 * would already be released in __lock_page_or_retry in mm/filemap.c.
 	 */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
+	if (fault_signal_pending(fault, regs)) {
 		if (!user_mode(regs))
 			goto no_context;
 		return;

arch/nios2/mm/fault.c +1 -1

index 6a2e716b959f..704ace8ca0ee 100644
@@ -133,7 +133,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/openrisc/mm/fault.c +1 -1

index 5d4d3a9691d0..85c7eb0c0186 100644
@@ -161,7 +161,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/parisc/mm/fault.c +1 -1

index adbd5e2144a3..f9be1d1cb43f 100644
@@ -304,7 +304,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
 
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/riscv/mm/fault.c +1 -1

index 96add1427a75..48a60e128b3f 100644
@@ -115,7 +115,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	 * signal first. We do not need to release the mmap_sem because it
 	 * would already be released in __lock_page_or_retry in mm/filemap.c.
 	 */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(tsk))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/s390/mm/fault.c +1 -2

index 7b0bb475c166..179cf92a56e5 100644
@@ -480,8 +480,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 	 * the fault.
 	 */
 	fault = handle_mm_fault(vma, address, flags);
-	/* No reason to continue if interrupted by SIGKILL. */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
+	if (fault_signal_pending(fault, regs)) {
 		fault = VM_FAULT_SIGNAL;
 		if (flags & FAULT_FLAG_RETRY_NOWAIT)
 			goto out_up;

arch/sparc/mm/fault_32.c +1 -1

index 8d69de111470..7a62edf7f68b 100644
@@ -237,7 +237,7 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/sparc/mm/fault_64.c +1 -1

index 2371fb6b97e4..d90bafb63e17 100644
@@ -421,7 +421,7 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
 
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		goto exit_exception;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

arch/unicore32/mm/fault.c +1 -1

index 76342de9cf8c..59d0e6ec2cfc 100644
@@ -250,7 +250,7 @@ static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	 * signal first. We do not need to release the mmap_sem because
 	 * it would already be released in __lock_page_or_retry in
 	 * mm/filemap.c. */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return 0;
 
 	if (!(fault & VM_FAULT_ERROR) && (flags & FAULT_FLAG_ALLOW_RETRY)) {

arch/xtensa/mm/fault.c +1 -1

index f81b1478da61..8651520de460 100644
@@ -110,7 +110,7 @@ void do_page_fault(struct pt_regs *regs)
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if (fault_signal_pending(fault, regs))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {

include/linux/sched/signal.h +13 -0

index efd8ce7675ed..46429192733b 100644
@@ -377,6 +377,19 @@ static inline int signal_pending_state(long state, struct task_struct *p)
 	return (state & TASK_INTERRUPTIBLE) || __fatal_signal_pending(p);
 }
 
+/*
+ * This should only be used in fault handlers to decide whether we
+ * should stop the current fault routine to handle the signals
+ * instead, especially with the case where we've got interrupted with
+ * a VM_FAULT_RETRY.
+ */
+static inline bool fault_signal_pending(unsigned int fault_flags,
+					struct pt_regs *regs)
+{
+	return unlikely((fault_flags & VM_FAULT_RETRY) &&
+			fatal_signal_pending(current));
+}
+
 /*
  * Reevaluate whether the task has signals pending delivery.
  * Wake the task if so.

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:39 UTC #4 lore raw

PATCH v5 4/16 x86/mm: Use helper fault_signal_pending()

In reply to Peter Xu

Let's move the fatal signal check even earlier so that we can directly use the new fault_signal_pending() in x86 mm code.

Signed-off-by Peter Xu <[email protected]>

---
 arch/x86/mm/fault.c | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

arch/x86/mm/fault.c +13 ~~-15~~

index 9ceacd1156db..059331797827 100644
@@ -1441,27 +1441,25 @@ void do_user_addr_fault(struct pt_regs *regs,
 	fault = handle_mm_fault(vma, address, flags);
 	major |= fault & VM_FAULT_MAJOR;
 
+	/* Quick path to respond to signals */
+	if (fault_signal_pending(fault, regs)) {
+		if (!user_mode(regs))
+			no_context(regs, hw_error_code, address, SIGBUS,
+				   BUS_ADRERR);
+		return;
+	}
+
 	/*
 	 * If we need to retry the mmap_sem has already been released,
 	 * and if there is a fatal signal pending there is no guarantee
 	 * that we made any progress. Handle this case first.
 	 */
-	if (unlikely(fault & VM_FAULT_RETRY)) {
+	if (unlikely((fault & VM_FAULT_RETRY) &&
+		     (flags & FAULT_FLAG_ALLOW_RETRY))) {
 		/* Retry at most once */
-		if (flags & FAULT_FLAG_ALLOW_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
-			flags |= FAULT_FLAG_TRIED;
-			if (!fatal_signal_pending(tsk))
-				goto retry;
-		}
-
-		/* User mode? Just return to handle the fatal exception */
-		if (flags & FAULT_FLAG_USER)
-			return;
-
-		/* Not returning to user mode? Handle exceptions or die: */
-		no_context(regs, hw_error_code, address, SIGBUS, BUS_ADRERR);
-		return;
+		flags &= ~FAULT_FLAG_ALLOW_RETRY;
+		flags |= FAULT_FLAG_TRIED;
+		goto retry;
 	}
 
 	up_read(&mm->mmap_sem);

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:40 UTC #5 lore raw

PATCH v5 5/16 arc/mm: Use helper fault_signal_pending()

In reply to Peter Xu

Let ARC to use the new helper fault_signal_pending() by moving the signal check out of the retry logic as standalone. This should also helps to simplify the code a bit.

Signed-off-by Peter Xu <[email protected]>

---
 arch/arc/mm/fault.c | 34 +++++++++++++---------------------
 1 file changed, 13 insertions(+), 21 deletions(-)

arch/arc/mm/fault.c +13 ~~-21~~

index 3861543b66a0..ee3ba7c7b891 100644
@@ -127,29 +127,21 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 
 	fault = handle_mm_fault(vma, address, flags);
 
+	/* Quick path to respond to signals */
+	if (fault_signal_pending(fault, regs)) {
+		if (!user_mode(regs))
+			goto no_context;
+		return;
+	}
+
 	/*
-	 * Fault retry nuances
+	 * Fault retry nuances, mmap_sem already relinquished by core mm
 	 */
-	if (unlikely(fault & VM_FAULT_RETRY)) {
-
-		/*
-		 * If fault needs to be retried, handle any pending signals
-		 * first (by returning to user mode).
-		 * mmap_sem already relinquished by core mm for RETRY case
-		 */
-		if (fatal_signal_pending(current)) {
-			if (!user_mode(regs))
-				goto no_context;
-			return;
-		}
-		/*
-		 * retry state machine
-		 */
-		if (flags & FAULT_FLAG_ALLOW_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
-			flags |= FAULT_FLAG_TRIED;
-			goto retry;
-		}
+	if (unlikely((fault & VM_FAULT_RETRY) &&
+		     (flags & FAULT_FLAG_ALLOW_RETRY))) {
+		flags &= ~FAULT_FLAG_ALLOW_RETRY;
+		flags |= FAULT_FLAG_TRIED;
+		goto retry;
 	}
 
 bad_area:

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:40 UTC #6 lore raw

PATCH v5 6/16 arm64/mm: Use helper fault_signal_pending()

In reply to Peter Xu

Let the arm64 fault handling to use the new fault_signal_pending() helper, by moving the signal handling out of the retry logic.

Signed-off-by Peter Xu <[email protected]>

---
 arch/arm64/mm/fault.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

arch/arm64/mm/fault.c +7 ~~-12~~

index cfd65b63f36f..4a695a44fb05 100644
@@ -477,19 +477,14 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 	fault = __do_page_fault(mm, addr, mm_flags, vm_flags);
 	major |= fault & VM_FAULT_MAJOR;
 
-	if (fault & VM_FAULT_RETRY) {
-		/*
-		 * If we need to retry but a fatal signal is pending,
-		 * handle the signal first. We do not need to release
-		 * the mmap_sem because it would already be released
-		 * in __lock_page_or_retry in mm/filemap.c.
-		 */
-		if (fatal_signal_pending(current)) {
-			if (!user_mode(regs))
-				goto no_context;
-			return 0;
-		}
+	/* Quick path to respond to signals */
+	if (fault_signal_pending(fault, regs)) {
+		if (!user_mode(regs))
+			goto no_context;
+		return 0;
+	}
 
+	if (fault & VM_FAULT_RETRY) {
 		/*
 		 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of
 		 * starvation.

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:40 UTC #7 lore raw

PATCH v5 7/16 powerpc/mm: Use helper fault_signal_pending()

In reply to Peter Xu

Let powerpc code to use the new helper, by moving the signal handling earlier before the retry logic.

Signed-off-by Peter Xu <[email protected]>

---
 arch/powerpc/mm/fault.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

arch/powerpc/mm/fault.c +4 -8

index 8432c281de92..7dabd1243f1b 100644
@@ -583,6 +583,9 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	major |= fault & VM_FAULT_MAJOR;
 
+	if (fault_signal_pending(fault, regs))
+		return user_mode(regs) ? 0 : SIGBUS;
+
 	/*
 	 * Handle the retry right now, the mmap_sem has been released in that
 	 * case.

@@ -596,15 +599,8 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 			 */
 			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
-			if (!fatal_signal_pending(current))
-				goto retry;
+			goto retry;
 		}
-
-		/*
-		 * User mode? Just return to handle the fatal exception otherwise
-		 * return to bad_page_fault
-		 */
-		return is_user ? 0 : SIGBUS;
 	}
 
 	up_read(&current->mm->mmap_sem);

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:40 UTC #8 lore raw

PATCH v5 8/16 sh/mm: Use helper fault_signal_pending()

In reply to Peter Xu

Let SH to use the new fault_signal_pending() helper. Here we'll need to move the up_read() out because that's actually needed as long as !RETRY cases. At the meantime we can drop all the rest of up_read()s now (which seems to be cleaner).

Signed-off-by Peter Xu <[email protected]>

---
 arch/sh/mm/fault.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

arch/sh/mm/fault.c +5 -5

index 5f51456f4fc7..eb4048ad0b38 100644
@@ -302,25 +302,25 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
 	 * Pagefault was interrupted by SIGKILL. We have no reason to
 	 * continue pagefault.
 	 */
-	if (fatal_signal_pending(current)) {
-		if (!(fault & VM_FAULT_RETRY))
-			up_read(&current->mm->mmap_sem);
+	if (fault_signal_pending(fault, regs)) {
 		if (!user_mode(regs))
 			no_context(regs, error_code, address);
 		return 1;
 	}
 
+	/* Release mmap_sem first if necessary */
+	if (!(fault & VM_FAULT_RETRY))
+		up_read(&current->mm->mmap_sem);
+
 	if (!(fault & VM_FAULT_ERROR))
 		return 0;
 
 	if (fault & VM_FAULT_OOM) {
 		/* Kernel mode? Handle exceptions or die: */
 		if (!user_mode(regs)) {
-			up_read(&current->mm->mmap_sem);
 			no_context(regs, error_code, address);
 			return 1;
 		}
-		up_read(&current->mm->mmap_sem);
 
 		/*
 		 * We ran out of memory, call the OOM killer, and return the

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:40 UTC #9 lore raw

PATCH v5 9/16 mm: Return faster for non-fatal signals in user mode faults

In reply to Peter Xu

The idea comes from the upstream discussion between Linus and Andrea:

https://lore.kernel.org/lkml/[email protected]/

A summary to the issue: there was a special path in handle_userfault() in the past that we'll return a VM_FAULT_NOPAGE when we detected non-fatal signals when waiting for userfault handling. We did that by reacquiring the mmap_sem before returning. However that brings a risk in that the vmas might have changed when we retake the mmap_sem and even we could be holding an invalid vma structure.

This patch is a preparation of removing that special path by allowing the page fault to return even faster if we were interrupted by a non-fatal signal during a user-mode page fault handling routine.

Signed-off-by Peter Xu <[email protected]>

---
 include/linux/sched/signal.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

include/linux/sched/signal.h +2 -1

index 46429192733b..031af0a6505a 100644
@@ -387,7 +387,8 @@ static inline bool fault_signal_pending(unsigned int fault_flags,
 					struct pt_regs *regs)
 {
 	return unlikely((fault_flags & VM_FAULT_RETRY) &&
-			fatal_signal_pending(current));
+			(fatal_signal_pending(current) ||
+			 (user_mode(regs) && signal_pending(current))));
 }
 
 /*

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:40 UTC #10 lore raw

PATCH v5 10/16 userfaultfd: Don't retake mmap_sem to emulate NOPAGE

In reply to Peter Xu

This patch removes the risk path in handle_userfault() then we will be sure that the callers of handle_mm_fault() will know that the VMAs might have changed. Meanwhile with previous patch we don't lose responsiveness as well since the core mm code now can handle the nonfatal userspace signals even if we return VM_FAULT_RETRY.

Reviewed-by Jerome Glisse <[email protected]>

Signed-off-by Peter Xu <[email protected]>

---
 fs/userfaultfd.c | 24 ------------------------
 1 file changed, 24 deletions(-)

fs/userfaultfd.c +0 ~~-24~~

index fe6d804a38dc..d8777146bae7 100644
@@ -524,30 +524,6 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 
 	__set_current_state(TASK_RUNNING);
 
-	if (return_to_userland) {
-		if (signal_pending(current) &&
-		    !fatal_signal_pending(current)) {
-			/*
-			 * If we got a SIGSTOP or SIGCONT and this is
-			 * a normal userland page fault, just let
-			 * userland return so the signal will be
-			 * handled and gdb debugging works.  The page
-			 * fault code immediately after we return from
-			 * this function is going to release the
-			 * mmap_sem and it's not depending on it
-			 * (unlike gup would if we were not to return
-			 * VM_FAULT_RETRY).
-			 *
-			 * If a fatal signal is pending we still take
-			 * the streamlined VM_FAULT_RETRY failure path
-			 * and there's no need to retake the mmap_sem
-			 * in such case.
-			 */
-			down_read(&mm->mmap_sem);
-			ret = VM_FAULT_NOPAGE;
-		}
-	}
-
 	/*
 	 * Here we race with the list_del; list_add in
 	 * userfaultfd_ctx_read(), however because we don't ever run

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:40 UTC #11 lore raw

PATCH v5 11/16 mm: Introduce FAULT_FLAG_DEFAULT

In reply to Peter Xu

Although there're tons of arch-specific page fault handlers, most of them are still sharing the same initial value of the page fault flags. Say, merely all of the page fault handlers would allow the fault to be retried, and they also allow the fault to respond to SIGKILL.

Let's define a default value for the fault flags to replace those initial page fault flags that were copied over. With this, it'll be far easier to introduce new fault flag that can be used by all the architectures instead of touching all the archs.

Reviewed-by David Hildenbrand <[email protected]>

Signed-off-by Peter Xu <[email protected]>

---
 arch/alpha/mm/fault.c      | 2 +-
 arch/arc/mm/fault.c        | 2 +-
 arch/arm/mm/fault.c        | 2 +-
 arch/arm64/mm/fault.c      | 2 +-
 arch/hexagon/mm/vm_fault.c | 2 +-
 arch/ia64/mm/fault.c       | 2 +-
 arch/m68k/mm/fault.c       | 2 +-
 arch/microblaze/mm/fault.c | 2 +-
 arch/mips/mm/fault.c       | 2 +-
 arch/nds32/mm/fault.c      | 2 +-
 arch/nios2/mm/fault.c      | 2 +-
 arch/openrisc/mm/fault.c   | 2 +-
 arch/parisc/mm/fault.c     | 2 +-
 arch/powerpc/mm/fault.c    | 2 +-
 arch/riscv/mm/fault.c      | 2 +-
 arch/s390/mm/fault.c       | 2 +-
 arch/sh/mm/fault.c         | 2 +-
 arch/sparc/mm/fault_32.c   | 2 +-
 arch/sparc/mm/fault_64.c   | 2 +-
 arch/um/kernel/trap.c      | 2 +-
 arch/unicore32/mm/fault.c  | 2 +-
 arch/x86/mm/fault.c        | 2 +-
 arch/xtensa/mm/fault.c     | 2 +-
 include/linux/mm.h         | 7 +++++++
 24 files changed, 30 insertions(+), 23 deletions(-)

arch/alpha/mm/fault.c +1 -1

index aea33b599037..fcfa229cc1e7 100644
@@ -89,7 +89,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
 	const struct exception_table_entry *fixup;
 	int si_code = SEGV_MAPERR;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	/* As of EV6, a load into $31/$f31 is a prefetch, and never faults
 	   (or is suppressed by the PALcode).  Support that for older CPUs

arch/arc/mm/fault.c +1 -1

index ee3ba7c7b891..33a609f1c43c 100644
@@ -94,7 +94,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 	         (regs->ecr_cause == ECR_C_PROTV_INST_FETCH))
 		exec = 1;
 
-	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	flags = FAULT_FLAG_DEFAULT;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
 	if (write)

arch/arm/mm/fault.c +1 -1

index c8f2950fa733..101ae6698637 100644
@@ -241,7 +241,7 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	struct mm_struct *mm;
 	int sig, code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	if (kprobe_page_fault(regs, fsr))
 		return 0;

arch/arm64/mm/fault.c +1 -1

index 4a695a44fb05..23e3feca0f02 100644
@@ -410,7 +410,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 	struct mm_struct *mm = current->mm;
 	vm_fault_t fault, major = 0;
 	unsigned long vm_flags = VM_READ | VM_WRITE;
-	unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int mm_flags = FAULT_FLAG_DEFAULT;
 
 	if (kprobe_page_fault(regs, esr))
 		return 0;

arch/hexagon/mm/vm_fault.c +1 -1

index d19beaf11b4c..d9e15d941bdb 100644
@@ -41,7 +41,7 @@ void do_page_fault(unsigned long address, long cause, struct pt_regs *regs)
 	int si_code = SEGV_MAPERR;
 	vm_fault_t fault;
 	const struct exception_table_entry *fixup;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	/*
 	 * If we're in an interrupt or have no user context,

arch/ia64/mm/fault.c +1 -1

index 211b4f439384..b5aa4e80c762 100644
@@ -65,7 +65,7 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
 	struct mm_struct *mm = current->mm;
 	unsigned long mask;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	mask = ((((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT)
 		| (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT));

arch/m68k/mm/fault.c +1 -1

index a455e202691b..182799fd9987 100644
@@ -71,7 +71,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct * vma;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	pr_debug("do page fault:\nregs->sr=%#x, regs->pc=%#lx, address=%#lx, %ld, %p\n",
 		regs->sr, regs->pc, address, error_code, mm ? mm->pgd : NULL);

arch/microblaze/mm/fault.c +1 -1

index cdde01dcdfc3..32da02778a63 100644
@@ -91,7 +91,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
 	int code = SEGV_MAPERR;
 	int is_write = error_code & ESR_S;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	regs->ear = address;
 	regs->esr = error_code;

arch/mips/mm/fault.c +1 -1

index 31fda59199eb..f811ef5efb80 100644
@@ -44,7 +44,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
 	const int field = sizeof(unsigned long) * 2;
 	int si_code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);

arch/nds32/mm/fault.c +1 -1

index c8f32b4784bd..4e402f2c88c3 100644
@@ -76,7 +76,7 @@ void do_page_fault(unsigned long entry, unsigned long addr,
 	int si_code;
 	vm_fault_t fault;
 	unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	error_code = error_code & (ITYPE_mskINST | ITYPE_mskETYPE);
 	tsk = current;

arch/nios2/mm/fault.c +1 -1

index 704ace8ca0ee..c38bea4220fb 100644
@@ -47,7 +47,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
 	struct mm_struct *mm = tsk->mm;
 	int code = SEGV_MAPERR;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	cause >>= 2;

arch/openrisc/mm/fault.c +1 -1

index 85c7eb0c0186..30d5c51e9d40 100644
@@ -50,7 +50,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 	struct vm_area_struct *vma;
 	int si_code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	tsk = current;

arch/parisc/mm/fault.c +1 -1

index f9be1d1cb43f..8e88e5c5f26a 100644
@@ -274,7 +274,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
 	if (!mm)
 		goto no_context;
 
-	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	flags = FAULT_FLAG_DEFAULT;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;

arch/powerpc/mm/fault.c +1 -1

index 7dabd1243f1b..db156537a2fa 100644
@@ -435,7 +435,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 {
 	struct vm_area_struct * vma;
 	struct mm_struct *mm = current->mm;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
  	int is_exec = TRAP(regs) == 0x400;
 	int is_user = user_mode(regs);
 	int is_write = page_fault_is_write(error_code);

arch/riscv/mm/fault.c +1 -1

index 48a60e128b3f..1f77dd2c491c 100644
@@ -28,7 +28,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	struct vm_area_struct *vma;
 	struct mm_struct *mm;
 	unsigned long addr, cause;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 	int code = SEGV_MAPERR;
 	vm_fault_t fault;

arch/s390/mm/fault.c +1 -1

index 179cf92a56e5..551ac311bd35 100644
@@ -429,7 +429,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 
 	address = trans_exc_code & __FAIL_ADDR_MASK;
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
-	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	flags = FAULT_FLAG_DEFAULT;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
 	if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)

arch/sh/mm/fault.c +1 -1

index eb4048ad0b38..d9c8f2d00a54 100644
@@ -380,7 +380,7 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
 	struct mm_struct *mm;
 	struct vm_area_struct * vma;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	tsk = current;
 	mm = tsk->mm;

arch/sparc/mm/fault_32.c +1 -1

index 7a62edf7f68b..447f61c4e996 100644
@@ -168,7 +168,7 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
 	int from_user = !(regs->psr & PSR_PS);
 	int code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	if (text_fault)
 		address = regs->pc;

arch/sparc/mm/fault_64.c +1 -1

index d90bafb63e17..6807fba66331 100644
@@ -267,7 +267,7 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
 	int si_code, fault_code;
 	vm_fault_t fault;
 	unsigned long address, mm_rss;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	fault_code = get_thread_fault_code();

arch/um/kernel/trap.c +1 -1

index 58fe36856182..bc2756782d64 100644
@@ -32,7 +32,7 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 	pmd_t *pmd;
 	pte_t *pte;
 	int err = -EFAULT;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	*code_out = SEGV_MAPERR;

arch/unicore32/mm/fault.c +1 -1

index 59d0e6ec2cfc..34a90453ca18 100644
@@ -202,7 +202,7 @@ static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	struct mm_struct *mm;
 	int sig, code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	tsk = current;
 	mm = tsk->mm;

arch/x86/mm/fault.c +1 -1

index 059331797827..d211585cfffd 100644
@@ -1287,7 +1287,7 @@ void do_user_addr_fault(struct pt_regs *regs,
 	struct task_struct *tsk;
 	struct mm_struct *mm;
 	vm_fault_t fault, major = 0;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	tsk = current;
 	mm = tsk->mm;

arch/xtensa/mm/fault.c +1 -1

index 8651520de460..6467e3fb9762 100644
@@ -43,7 +43,7 @@ void do_page_fault(struct pt_regs *regs)
 
 	int is_write, is_exec;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	code = SEGV_MAPERR;

include/linux/mm.h +7 -0

index 0334ca97c584..57fb5c535f8e 100644
@@ -393,6 +393,13 @@ extern pgprot_t protection_map[16];
 #define FAULT_FLAG_REMOTE	0x80	/* faulting for non current tsk/mm */
 #define FAULT_FLAG_INSTRUCTION  0x100	/* The fault was during an instruction fetch */
 
+/*
+ * The default fault flags that should be used by most of the
+ * arch-specific page fault handlers.
+ */
+#define FAULT_FLAG_DEFAULT  (FAULT_FLAG_ALLOW_RETRY | \
+			     FAULT_FLAG_KILLABLE)
+
 #define FAULT_FLAG_TRACE \
 	{ FAULT_FLAG_WRITE,		"WRITE" }, \
 	{ FAULT_FLAG_MKWRITE,		"MKWRITE" }, \

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:41 UTC #12 lore raw

PATCH v5 12/16 mm: Introduce FAULT_FLAG_INTERRUPTIBLE

In reply to Peter Xu

handle_userfaultfd() is currently the only one place in the kernel page fault procedures that can respond to non-fatal userspace signals. It was trying to detect such an allowance by checking against USER & KILLABLE flags, which was "un-official".

In this patch, we introduced a new flag (FAULT_FLAG_INTERRUPTIBLE) to show that the fault handler allows the fault procedure to respond even to non-fatal signals. Meanwhile, add this new flag to the default fault flags so that all the page fault handlers can benefit from the new flag. With that, replacing the userfault check to this one.

Since the line is getting even longer, clean up the fault flags a bit too to ease TTY users.

Although we've got a new flag and applied it, we shouldn't have any functional change with this patch so far.

Reviewed-by David Hildenbrand <[email protected]>

Signed-off-by Peter Xu <[email protected]>

---
 fs/userfaultfd.c   |  4 +---
 include/linux/mm.h | 39 ++++++++++++++++++++++++++++-----------
 2 files changed, 29 insertions(+), 14 deletions(-)

fs/userfaultfd.c +1 -3

index d8777146bae7..2b3b48e94ae4 100644
@@ -462,9 +462,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	uwq.ctx = ctx;
 	uwq.waken = false;
 
-	return_to_userland =
-		(vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
-		(FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
+	return_to_userland = vmf->flags & FAULT_FLAG_INTERRUPTIBLE;
 	blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
 			 TASK_KILLABLE;

include/linux/mm.h +28 ~~-11~~

index 57fb5c535f8e..53ec7abb8472 100644
@@ -383,22 +383,38 @@ extern unsigned int kobjsize(const void *objp);
  */
 extern pgprot_t protection_map[16];
 
-#define FAULT_FLAG_WRITE	0x01	/* Fault was a write access */
-#define FAULT_FLAG_MKWRITE	0x02	/* Fault was mkwrite of existing pte */
-#define FAULT_FLAG_ALLOW_RETRY	0x04	/* Retry fault if blocking */
-#define FAULT_FLAG_RETRY_NOWAIT	0x08	/* Don't drop mmap_sem and wait when retrying */
-#define FAULT_FLAG_KILLABLE	0x10	/* The fault task is in SIGKILL killable region */
-#define FAULT_FLAG_TRIED	0x20	/* Second try */
-#define FAULT_FLAG_USER		0x40	/* The fault originated in userspace */
-#define FAULT_FLAG_REMOTE	0x80	/* faulting for non current tsk/mm */
-#define FAULT_FLAG_INSTRUCTION  0x100	/* The fault was during an instruction fetch */
+/**
+ * Fault flag definitions.
+ *
+ * @FAULT_FLAG_WRITE: Fault was a write fault.
+ * @FAULT_FLAG_MKWRITE: Fault was mkwrite of existing PTE.
+ * @FAULT_FLAG_ALLOW_RETRY: Allow to retry the fault if blocked.
+ * @FAULT_FLAG_RETRY_NOWAIT: Don't drop mmap_sem and wait when retrying.
+ * @FAULT_FLAG_KILLABLE: The fault task is in SIGKILL killable region.
+ * @FAULT_FLAG_TRIED: The fault has been tried once.
+ * @FAULT_FLAG_USER: The fault originated in userspace.
+ * @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
+ * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
+ * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
+ */
+#define FAULT_FLAG_WRITE			0x01
+#define FAULT_FLAG_MKWRITE			0x02
+#define FAULT_FLAG_ALLOW_RETRY			0x04
+#define FAULT_FLAG_RETRY_NOWAIT			0x08
+#define FAULT_FLAG_KILLABLE			0x10
+#define FAULT_FLAG_TRIED			0x20
+#define FAULT_FLAG_USER				0x40
+#define FAULT_FLAG_REMOTE			0x80
+#define FAULT_FLAG_INSTRUCTION  		0x100
+#define FAULT_FLAG_INTERRUPTIBLE		0x200
 
 /*
  * The default fault flags that should be used by most of the
  * arch-specific page fault handlers.
  */
 #define FAULT_FLAG_DEFAULT  (FAULT_FLAG_ALLOW_RETRY | \
-			     FAULT_FLAG_KILLABLE)
+			     FAULT_FLAG_KILLABLE | \
+			     FAULT_FLAG_INTERRUPTIBLE)
 
 #define FAULT_FLAG_TRACE \
 	{ FAULT_FLAG_WRITE,		"WRITE" }, \

@@ -409,7 +425,8 @@ extern pgprot_t protection_map[16];
 	{ FAULT_FLAG_TRIED,		"TRIED" }, \
 	{ FAULT_FLAG_USER,		"USER" }, \
 	{ FAULT_FLAG_REMOTE,		"REMOTE" }, \
-	{ FAULT_FLAG_INSTRUCTION,	"INSTRUCTION" }
+	{ FAULT_FLAG_INSTRUCTION,	"INSTRUCTION" }, \
+	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }
 
 /*
  * vm_fault is filled by the the pagefault handler and passed to the vma's

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:41 UTC #13 lore raw

PATCH v5 13/16 mm: Allow VM_FAULT_RETRY for multiple times

In reply to Peter Xu

The idea comes from a discussion between Linus and Andrea [1].

Before this patch we only allow a page fault to retry once. We achieved this by clearing the FAULT_FLAG_ALLOW_RETRY flag when doing handle_mm_fault() the second time. This was majorly used to avoid unexpected starvation of the system by looping over forever to handle the page fault on a single page. However that should hardly happen, and after all for each code path to return a VM_FAULT_RETRY we'll first wait for a condition (during which time we should possibly yield the cpu) to happen before VM_FAULT_RETRY is really returned.

This patch removes the restriction by keeping the FAULT_FLAG_ALLOW_RETRY flag when we receive VM_FAULT_RETRY. It means that the page fault handler now can retry the page fault for multiple times if necessary without the need to generate another page fault event. Meanwhile we still keep the FAULT_FLAG_TRIED flag so page fault handler can still identify whether a page fault is the first attempt or not.

Then we'll have these combinations of fault flags (only considering ALLOW_RETRY flag and TRIED flag):

- ALLOW_RETRY and !TRIED: this means the page fault allows to retry, and this is the first try

- ALLOW_RETRY and TRIED: this means the page fault allows to
retry, and this is not the first try

- !ALLOW_RETRY and !TRIED: this means the page fault does not allow to retry at all

- !ALLOW_RETRY and TRIED: this is forbidden and should never be used

In existing code we have multiple places that has taken special care of the first condition above by checking against (fault_flags & FAULT_FLAG_ALLOW_RETRY). This patch introduces a simple helper to detect the first retry of a page fault by checking against both (fault_flags & FAULT_FLAG_ALLOW_RETRY) and !(fault_flag & FAULT_FLAG_TRIED) because now even the 2nd try will have the ALLOW_RETRY set, then use that helper in all existing special paths. One example is in __lock_page_or_retry(), now we'll drop the mmap_sem only in the first attempt of page fault and we'll keep it in follow up retries, so old locking behavior will be retained.

This will be a nice enhancement for current code [2] at the same time a supporting material for the future userfaultfd-writeprotect work, since in that work there will always be an explicit userfault writeprotect retry for protected pages, and if that cannot resolve the page fault (e.g., when userfaultfd-writeprotect is used in conjunction with swapped pages) then we'll possibly need a 3rd retry of the page fault. It might also benefit other potential users who will have similar requirement like userfault write-protection.

GUP code is not touched yet and will be covered in follow up patch.

Please read the thread below for more information.

[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/lkml/[email protected]/

Reviewed-by Jerome Glisse <[email protected]>

Signed-off-by Peter Xu <[email protected]>

---
 arch/alpha/mm/fault.c           |  2 +-
 arch/arc/mm/fault.c             |  1 -
 arch/arm/mm/fault.c             |  3 ---
 arch/arm64/mm/fault.c           |  5 -----
 arch/hexagon/mm/vm_fault.c      |  1 -
 arch/ia64/mm/fault.c            |  1 -
 arch/m68k/mm/fault.c            |  3 ---
 arch/microblaze/mm/fault.c      |  1 -
 arch/mips/mm/fault.c            |  1 -
 arch/nds32/mm/fault.c           |  1 -
 arch/nios2/mm/fault.c           |  3 ---
 arch/openrisc/mm/fault.c        |  1 -
 arch/parisc/mm/fault.c          |  4 +---
 arch/powerpc/mm/fault.c         |  6 ------
 arch/riscv/mm/fault.c           |  5 -----
 arch/s390/mm/fault.c            |  5 +----
 arch/sh/mm/fault.c              |  1 -
 arch/sparc/mm/fault_32.c        |  1 -
 arch/sparc/mm/fault_64.c        |  1 -
 arch/um/kernel/trap.c           |  1 -
 arch/unicore32/mm/fault.c       |  4 +---
 arch/x86/mm/fault.c             |  2 --
 arch/xtensa/mm/fault.c          |  1 -
 drivers/gpu/drm/ttm/ttm_bo_vm.c | 12 ++++++++---
 include/linux/mm.h              | 37 +++++++++++++++++++++++++++++++++
 mm/filemap.c                    |  2 +-
 mm/shmem.c                      |  2 +-
 27 files changed, 52 insertions(+), 55 deletions(-)

arch/alpha/mm/fault.c +1 -1

index fcfa229cc1e7..c2d7b6d7bac7 100644
@@ -169,7 +169,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
+			flags |= FAULT_FLAG_TRIED;
 
 			 /* No need to up_read(&mm->mmap_sem) as we would
 			 * have already released it in __lock_page_or_retry

arch/arc/mm/fault.c +0 -1

index 33a609f1c43c..fdf09db1581d 100644
@@ -139,7 +139,6 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 	 */
 	if (unlikely((fault & VM_FAULT_RETRY) &&
 		     (flags & FAULT_FLAG_ALLOW_RETRY))) {
-		flags &= ~FAULT_FLAG_ALLOW_RETRY;
 		flags |= FAULT_FLAG_TRIED;
 		goto retry;
 	}

arch/arm/mm/fault.c +0 -3

index 101ae6698637..952bd9d7487d 100644
@@ -319,9 +319,6 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 					regs, addr);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			* of starvation. */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}

arch/arm64/mm/fault.c +0 -5

index 23e3feca0f02..b6badba3a677 100644
@@ -485,12 +485,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 	}
 
 	if (fault & VM_FAULT_RETRY) {
-		/*
-		 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of
-		 * starvation.
-		 */
 		if (mm_flags & FAULT_FLAG_ALLOW_RETRY) {
-			mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			mm_flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}

arch/hexagon/mm/vm_fault.c +0 -1

index d9e15d941bdb..72334b26317a 100644
@@ -102,7 +102,6 @@ void do_page_fault(unsigned long address, long cause, struct pt_regs *regs)
 			else
 				current->min_flt++;
 			if (fault & VM_FAULT_RETRY) {
-				flags &= ~FAULT_FLAG_ALLOW_RETRY;
 				flags |= FAULT_FLAG_TRIED;
 				goto retry;
 			}

arch/ia64/mm/fault.c +0 -1

index b5aa4e80c762..30d0c1fca99e 100644
@@ -167,7 +167,6 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			 /* No need to up_read(&mm->mmap_sem) as we would

arch/m68k/mm/fault.c +0 -3

index 182799fd9987..f7afb9897966 100644
@@ -162,9 +162,6 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation. */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*

arch/microblaze/mm/fault.c +0 -1

index 32da02778a63..3248141f8ed5 100644
@@ -236,7 +236,6 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*

arch/mips/mm/fault.c +0 -1

index f811ef5efb80..02ae0c87301f 100644
@@ -178,7 +178,6 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
 			tsk->min_flt++;
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*

arch/nds32/mm/fault.c +0 -1

index 4e402f2c88c3..52097d5f63c6 100644
@@ -242,7 +242,6 @@ void do_page_fault(unsigned long entry, unsigned long addr,
 				      1, regs, addr);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/* No need to up_read(&mm->mmap_sem) as we would

arch/nios2/mm/fault.c +0 -3

index c38bea4220fb..ec9d8a9c426f 100644
@@ -157,9 +157,6 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation. */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*

arch/openrisc/mm/fault.c +0 -1

index 30d5c51e9d40..8af1cc78c4fb 100644
@@ -181,7 +181,6 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 		else
 			tsk->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			 /* No need to up_read(&mm->mmap_sem) as we would

arch/parisc/mm/fault.c +1 -3

index 8e88e5c5f26a..86e8c848f3d7 100644
@@ -328,14 +328,12 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
-
 			/*
 			 * No need to up_read(&mm->mmap_sem) as we would
 			 * have already released it in __lock_page_or_retry
 			 * in mm/filemap.c.
 			 */
-
+			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
 	}

arch/powerpc/mm/fault.c +0 -6

index db156537a2fa..65cc735045bb 100644
@@ -591,13 +591,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 	 * case.
 	 */
 	if (unlikely(fault & VM_FAULT_RETRY)) {
-		/* We retry only once */
 		if (flags & FAULT_FLAG_ALLOW_RETRY) {
-			/*
-			 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation.
-			 */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}

arch/riscv/mm/fault.c +0 -5

index 1f77dd2c491c..12954f02cf02 100644
@@ -142,11 +142,6 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 				      1, regs, addr);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			/*
-			 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation.
-			 */
-			flags &= ~(FAULT_FLAG_ALLOW_RETRY);
 			flags |= FAULT_FLAG_TRIED;
 
 			/*

arch/s390/mm/fault.c +1 -4

index 551ac311bd35..aeccdb30899a 100644
@@ -513,10 +513,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 				fault = VM_FAULT_PFAULT;
 				goto out_up;
 			}
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation. */
-			flags &= ~(FAULT_FLAG_ALLOW_RETRY |
-				   FAULT_FLAG_RETRY_NOWAIT);
+			flags &= ~FAULT_FLAG_RETRY_NOWAIT;
 			flags |= FAULT_FLAG_TRIED;
 			down_read(&mm->mmap_sem);
 			goto retry;

arch/sh/mm/fault.c +0 -1

index d9c8f2d00a54..13ee4d20e622 100644
@@ -481,7 +481,6 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
 				      regs, address);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*

arch/sparc/mm/fault_32.c +0 -1

index 447f61c4e996..a8c8cb3b891f 100644
@@ -261,7 +261,6 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
 				      1, regs, address);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/* No need to up_read(&mm->mmap_sem) as we would

arch/sparc/mm/fault_64.c +0 -1

index 6807fba66331..eb4cfd5634e2 100644
@@ -445,7 +445,6 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
 				      1, regs, address);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/* No need to up_read(&mm->mmap_sem) as we would

arch/um/kernel/trap.c +0 -1

index bc2756782d64..4bcf5873e931 100644
@@ -96,7 +96,6 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 			else
 				current->min_flt++;
 			if (fault & VM_FAULT_RETRY) {
-				flags &= ~FAULT_FLAG_ALLOW_RETRY;
 				flags |= FAULT_FLAG_TRIED;
 
 				goto retry;

arch/unicore32/mm/fault.c +1 -3

index 34a90453ca18..a9bd08fbe588 100644
@@ -259,9 +259,7 @@ static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 		else
 			tsk->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			* of starvation. */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
+			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
 	}

arch/x86/mm/fault.c +0 -2

index d211585cfffd..55e749af8a61 100644
@@ -1456,8 +1456,6 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 */
 	if (unlikely((fault & VM_FAULT_RETRY) &&
 		     (flags & FAULT_FLAG_ALLOW_RETRY))) {
-		/* Retry at most once */
-		flags &= ~FAULT_FLAG_ALLOW_RETRY;
 		flags |= FAULT_FLAG_TRIED;
 		goto retry;
 	}

arch/xtensa/mm/fault.c +0 -1

index 6467e3fb9762..c97c2c84d14a 100644
@@ -128,7 +128,6 @@ void do_page_fault(struct pt_regs *regs)
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			 /* No need to up_read(&mm->mmap_sem) as we would

drivers/gpu/drm/ttm/ttm_bo_vm.c +9 -3

index 6dacff49c1cc..8f2f9ee6effa 100644
@@ -61,9 +61,10 @@ static vm_fault_t ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
 
 	/*
 	 * If possible, avoid waiting for GPU with mmap_sem
-	 * held.
+	 * held.  We only do this if the fault allows retry and this
+	 * is the first attempt.
 	 */
-	if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
+	if (fault_flag_allow_retry_first(vmf->flags)) {
 		ret = VM_FAULT_RETRY;
 		if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
 			goto out_unlock;

@@ -132,7 +133,12 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
 	 * for the buffer to become unreserved.
 	 */
 	if (unlikely(!reservation_object_trylock(bo->resv))) {
-		if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
+		/*
+		 * If the fault allows retry and this is the first
+		 * fault attempt, we try to release the mmap_sem
+		 * before waiting
+		 */
+		if (fault_flag_allow_retry_first(vmf->flags)) {
 			if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
 				ttm_bo_get(bo);
 				up_read(&vmf->vma->vm_mm->mmap_sem);

include/linux/mm.h +37 -0

index 53ec7abb8472..0fdbdcb257d6 100644
@@ -396,6 +396,25 @@ extern pgprot_t protection_map[16];
  * @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
  * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
  * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
+ *
+ * About @FAULT_FLAG_ALLOW_RETRY and @FAULT_FLAG_TRIED: we can specify
+ * whether we would allow page faults to retry by specifying these two
+ * fault flags correctly.  Currently there can be three legal combinations:
+ *
+ * (a) ALLOW_RETRY and !TRIED:  this means the page fault allows retry, and
+ *                              this is the first try
+ *
+ * (b) ALLOW_RETRY and TRIED:   this means the page fault allows retry, and
+ *                              we've already tried at least once
+ *
+ * (c) !ALLOW_RETRY and !TRIED: this means the page fault does not allow retry
+ *
+ * The unlisted combination (!ALLOW_RETRY && TRIED) is illegal and should never
+ * be used.  Note that page faults can be allowed to retry for multiple times,
+ * in which case we'll have an initial fault with flags (a) then later on
+ * continuous faults with flags (b).  We should always try to detect pending
+ * signals before a retry to make sure the continuous page faults can still be
+ * interrupted if necessary.
  */
 #define FAULT_FLAG_WRITE			0x01
 #define FAULT_FLAG_MKWRITE			0x02

@@ -416,6 +435,24 @@ extern pgprot_t protection_map[16];
 			     FAULT_FLAG_KILLABLE | \
 			     FAULT_FLAG_INTERRUPTIBLE)
 
+/**
+ * fault_flag_allow_retry_first - check ALLOW_RETRY the first time
+ *
+ * This is mostly used for places where we want to try to avoid taking
+ * the mmap_sem for too long a time when waiting for another condition
+ * to change, in which case we can try to be polite to release the
+ * mmap_sem in the first round to avoid potential starvation of other
+ * processes that would also want the mmap_sem.
+ *
+ * Return: true if the page fault allows retry and this is the first
+ * attempt of the fault handling; false otherwise.
+ */
+static inline bool fault_flag_allow_retry_first(unsigned int flags)
+{
+	return (flags & FAULT_FLAG_ALLOW_RETRY) &&
+	    (!(flags & FAULT_FLAG_TRIED));
+}
+
 #define FAULT_FLAG_TRACE \
 	{ FAULT_FLAG_WRITE,		"WRITE" }, \
 	{ FAULT_FLAG_MKWRITE,		"MKWRITE" }, \

mm/filemap.c +1 -1

index d0cf700bf201..543404617f5a 100644
@@ -1399,7 +1399,7 @@ EXPORT_SYMBOL_GPL(__lock_page_killable);
 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
 			 unsigned int flags)
 {
-	if (flags & FAULT_FLAG_ALLOW_RETRY) {
+	if (fault_flag_allow_retry_first(flags)) {
 		/*
 		 * CAUTION! In this case, mmap_sem is not released
 		 * even though return 0.

mm/shmem.c +1 -1

index 2bed4761f279..1af8d8e60231 100644
@@ -2011,7 +2011,7 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
 			DEFINE_WAIT_FUNC(shmem_fault_wait, synchronous_wake_function);
 
 			ret = VM_FAULT_NOPAGE;
-			if ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) &&
+			if (fault_flag_allow_retry_first(vmf->flags) &&
 			   !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
 				/* It's polite to up mmap_sem if we can */
 				up_read(&vma->vm_mm->mmap_sem);

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:41 UTC #14 lore raw

PATCH v5 14/16 mm/gup: Allow VM_FAULT_RETRY for multiple times

In reply to Peter Xu

This is the gup counterpart of the change that allows the VM_FAULT_RETRY to happen for more than once. One thing to mention is that we must check the fatal signal here before retry because the GUP can be interrupted by that, otherwise we can loop forever.

Signed-off-by Peter Xu <[email protected]>

---
 mm/gup.c     | 27 +++++++++++++++++++++------
 mm/hugetlb.c |  6 ++++--
 2 files changed, 25 insertions(+), 8 deletions(-)

mm/gup.c +21 -6

index e60d32f1674d..d2811bb15a25 100644
@@ -644,7 +644,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 	if (*flags & FOLL_TRIED) {
-		VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
+		/*
+		 * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
+		 * can co-exist
+		 */
 		fault_flags |= FAULT_FLAG_TRIED;
 	}

@@ -994,7 +997,6 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
 		down_read(&mm->mmap_sem);
 		if (!(fault_flags & FAULT_FLAG_TRIED)) {
 			*unlocked = true;
-			fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			fault_flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}

@@ -1069,17 +1071,30 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 		if (likely(pages))
 			pages += ret;
 		start += ret << PAGE_SHIFT;
+		lock_dropped = true;
 
+retry:
 		/*
 		 * Repeat on the address that fired VM_FAULT_RETRY
-		 * without FAULT_FLAG_ALLOW_RETRY but with
-		 * FAULT_FLAG_TRIED.
+		 * with both FAULT_FLAG_ALLOW_RETRY and
+		 * FAULT_FLAG_TRIED.  Note that GUP can be interrupted
+		 * by fatal signals, so we need to check it before we
+		 * start trying again otherwise it can loop forever.
 		 */
+
+		if (fatal_signal_pending(current))
+			break;
+
 		*locked = 1;
-		lock_dropped = true;
 		down_read(&mm->mmap_sem);
+
 		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
-				       pages, NULL, NULL);
+				       pages, NULL, locked);
+		if (!*locked) {
+			/* Continue to retry until we succeeded */
+			BUG_ON(ret != 0);
+			goto retry;
+		}
 		if (ret != 1) {
 			BUG_ON(ret > 1);
 			if (!pages_done)

mm/hugetlb.c +4 -2

index 31c2a6275023..d0c98cff5b0f 100644
@@ -4347,8 +4347,10 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
 					FAULT_FLAG_RETRY_NOWAIT;
 			if (flags & FOLL_TRIED) {
-				VM_WARN_ON_ONCE(fault_flags &
-						FAULT_FLAG_ALLOW_RETRY);
+				/*
+				 * Note: FAULT_FLAG_ALLOW_RETRY and
+				 * FAULT_FLAG_TRIED can co-exist
+				 */
 				fault_flags |= FAULT_FLAG_TRIED;
 			}
 			ret = hugetlb_fault(mm, vma, vaddr, fault_flags);

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:41 UTC #15 lore raw

PATCH v5 15/16 mm/gup: Allow to react to fatal signals

In reply to Peter Xu

The existing gup code does not react to the fatal signals in many code paths. For example, in one retry path of gup we're still using down_read() rather than down_read_killable(). Also, when doing page faults we don't pass in FAULT_FLAG_KILLABLE as well, which means that within the faulting process we'll wait in non-killable way as well. These were spotted by Linus during the code review of some other patches.

Let's allow the gup code to react to fatal signals to improve the responsiveness of threads when during gup and being killed.

Signed-off-by Peter Xu <[email protected]>

---
 mm/gup.c     | 12 +++++++++---
 mm/hugetlb.c |  3 ++-
 2 files changed, 11 insertions(+), 4 deletions(-)

mm/gup.c +9 -3

index d2811bb15a25..4c638473db83 100644
@@ -640,7 +640,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	if (*flags & FOLL_REMOTE)
 		fault_flags |= FAULT_FLAG_REMOTE;
 	if (locked)
-		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 	if (*flags & FOLL_TRIED) {

@@ -973,7 +973,7 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
 	vm_fault_t ret, major = 0;
 
 	if (unlocked)
-		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 
 retry:
 	vma = find_extend_vma(mm, address);

@@ -1086,7 +1086,13 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 			break;
 
 		*locked = 1;
-		down_read(&mm->mmap_sem);
+		ret = down_read_killable(&mm->mmap_sem);
+		if (ret) {
+			BUG_ON(ret > 0);
+			if (!pages_done)
+				pages_done = ret;
+			break;
+		}
 
 		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
 				       pages, NULL, locked);

mm/hugetlb.c +2 -1

index d0c98cff5b0f..84034154d50e 100644
@@ -4342,7 +4342,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			if (flags & FOLL_WRITE)
 				fault_flags |= FAULT_FLAG_WRITE;
 			if (locked)
-				fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
+					FAULT_FLAG_KILLABLE;
 			if (flags & FOLL_NOWAIT)
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
 					FAULT_FLAG_RETRY_NOWAIT;

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-26 09:41 UTC #16 lore raw

PATCH v5 16/16 mm/userfaultfd: Honor FAULT_FLAG_KILLABLE in fault path

In reply to Peter Xu

Userfaultfd fault path was by default killable even if the caller does not have FAULT_FLAG_KILLABLE. That makes sense before in that when with gup we don't have FAULT_FLAG_KILLABLE properly set before. Now after previous patch we've got FAULT_FLAG_KILLABLE applied even for gup code so it should also make sense to let userfaultfd to honor the FAULT_FLAG_KILLABLE.

Because we're unconditionally setting FAULT_FLAG_KILLABLE in gup code right now, this patch should have no functional change. It also cleaned the code a little bit by introducing some helpers.

Signed-off-by Peter Xu <[email protected]>

---
 fs/userfaultfd.c | 36 ++++++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)

fs/userfaultfd.c +28 -8

index 2b3b48e94ae4..8c5863ccbf0e 100644
@@ -334,6 +334,30 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
 	return ret;
 }
 
+/* Should pair with userfaultfd_signal_pending() */
+static inline long userfaultfd_get_blocking_state(unsigned int flags)
+{
+	if (flags & FAULT_FLAG_INTERRUPTIBLE)
+		return TASK_INTERRUPTIBLE;
+
+	if (flags & FAULT_FLAG_KILLABLE)
+		return TASK_KILLABLE;
+
+	return TASK_UNINTERRUPTIBLE;
+}
+
+/* Should pair with userfaultfd_get_blocking_state() */
+static inline bool userfaultfd_signal_pending(unsigned int flags)
+{
+	if (flags & FAULT_FLAG_INTERRUPTIBLE)
+		return signal_pending(current);
+
+	if (flags & FAULT_FLAG_KILLABLE)
+		return fatal_signal_pending(current);
+
+	return false;
+}
+
 /*
  * The locking rules involved in returning VM_FAULT_RETRY depending on
  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and

@@ -355,7 +379,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	struct userfaultfd_ctx *ctx;
 	struct userfaultfd_wait_queue uwq;
 	vm_fault_t ret = VM_FAULT_SIGBUS;
-	bool must_wait, return_to_userland;
+	bool must_wait;
 	long blocking_state;
 
 	/*

@@ -462,9 +486,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	uwq.ctx = ctx;
 	uwq.waken = false;
 
-	return_to_userland = vmf->flags & FAULT_FLAG_INTERRUPTIBLE;
-	blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
-			 TASK_KILLABLE;
+	blocking_state = userfaultfd_get_blocking_state(vmf->flags);
 
 	spin_lock_irq(&ctx->fault_pending_wqh.lock);
 	/*

@@ -490,8 +512,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	up_read(&mm->mmap_sem);
 
 	if (likely(must_wait && !READ_ONCE(ctx->released) &&
-		   (return_to_userland ? !signal_pending(current) :
-		    !fatal_signal_pending(current)))) {
+		   userfaultfd_signal_pending(vmf->flags))) {
 		wake_up_poll(&ctx->fd_wqh, EPOLLIN);
 		schedule();
 		ret |= VM_FAULT_MAJOR;

@@ -513,8 +534,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 			set_current_state(blocking_state);
 			if (READ_ONCE(uwq.waken) ||
 			    READ_ONCE(ctx->released) ||
-			    (return_to_userland ? signal_pending(current) :
-			     fatal_signal_pending(current)))
+			    userfaultfd_signal_pending(vmf->flags))
 				break;
 			schedule();
 		}

Signature · 1 line

2.21.0

Peter Xu

author reviewer

2019-09-29 09:17 UTC #17 lore raw

Re: [PATCH v5 16/16] mm/userfaultfd: Honor FAULT_FLAG_KILLABLE in fault path

fs/userfaultfd.c vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) · line 515

Quoted 7 lines · Peter Xu

fs/userfaultfd.c +1 -2

@@ -490,8 +512,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	up_read(&mm->mmap_sem);
 
 	if (likely(must_wait && !READ_ONCE(ctx->released) &&
-		   (return_to_userland ? !signal_pending(current) :
-		    !fatal_signal_pending(current)))) {
+		   userfaultfd_signal_pending(vmf->flags))) {

Sorry, here it should be "!userfaultfd_signal_pending(vmf->flags)".

Signature · 1 line

Peter Xu

Peter Xu

author reviewer

2019-10-14 08:41 UTC #18 lore raw

In reply to Peter Xu

Quoted 25 lines · Peter Xu

This is v5 of the series. As Matthew suggested, I split the previous patch "mm: Return faster for non-fatal signals in user mode faults" into a few smaller ones:
1. One patch to introduce fatal_signal_pending(), and use it in archs that can directly apply
2. A few more patches to let the rest archs to use the new helper. With that we can have an unified entry for signal detection
3. One last patch to change fatal_signal_pending() to detect userspace non-fatal signal
Nothing should have changed in the rest patches. Because the fault retry patches will depend on the previous ones, I decided to simply repost all the patches.
Here's the new patchset layout:
Patch 1-2: cleanup, and potential bugfix of hugetlbfs on fault retry
Patch 3-9: let page fault to respond to non-fatal signals faster
Patch 10: remove the userfaultfd NOPAGE emulation

Quoted 7 lines

Patch 11-14: allow page fault to retry more than once
Patch 15-16: let gup code to use FAULT_FLAG_KILLABLE too
I would really appreciate any review comments for the series, especially for the first two patches which IMHO are even not related to this patchset and they should either cleanup or fix things.

Ping..

IMHO this series should fix some real issues, e.g., the whole series targets to fix things like [1] or as patch 2 might fix potential bugs. I'd appreciate if it can get some more review comments.

I didn't repost because the last patch only need a one-line change so I assume it does not affect the most rest of reviews. I can repost if anyone would like me to.

Thanks,

[1] https://lore.kernel.org/lkml/[email protected]/

Signature · 1 line

Peter Xu