mm: Page fault enhancements

[Resend v6]

This is v6 of the series. It is majorly a rebase to 5.6-rc2, nothing else to be expected (plus some tests after the rebase). Instead of rewrite the cover letter I decided to use what we have for v5.

Adding extra CCs for both Bobby Powers <[email protected]> and Brian Geffon <[email protected]>.

Online repo: https://github.com/xzpeter/linux/tree/mm-pf-signal-retry

Any review comment is appreciated. Thanks,

=============== v5 cover letter ==================

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/internal.h                   |  6 +--
 31 files changed, 281 insertions(+), 240 deletions(-)

2.24.1