arm: mm: Fix definition of pmd_mknotpresent

PATCH New Steve Capper 3 participants 4 messages Mar 2, 2016 Arm (32-bit)

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Steve Capper

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2016-03-02 01:03 UTC #0 lore raw

PATCH 1/1 arm: mm: Fix definition of pmd_mknotpresent

Currently pmd_mknotpresent will use a zero entry to respresent an invalidated pmd.

Unfortunately this definition clashes with pmd_none, thus it is possible for a race condition to occur if zap_pmd_range sees pmd_none whilst __split_huge_pmd_locked is running too with pmdp_invalidate just called.

This patch fixes the race condition by modifying pmd_mknotpresent to create non-zero faulting entries (as is done in other architectures), removing the ambiguity with pmd_none.

Fixes 8d9625070073 ("ARM: mm: Transparent huge page support for LPAE systems.")

Reported-by Kirill A. Shutemov <[email protected]>

Signed-off-by Steve Capper <[email protected]>

Acked-by Will Deacon <[email protected]>

---

This patch addresses an issue discussed at:
http://lkml.iu.edu/hypermail/linux/kernel/1602.3/01846.html

---
 arch/arm/include/asm/pgtable-3level.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

arch/arm/include/asm/pgtable-3level.h +2 -2

index dc46398..451b6e7 100644
@@ -249,10 +249,10 @@ PMD_BIT_FUNC(mkyoung,   |= PMD_SECT_AF);
 #define pfn_pmd(pfn,prot)	(__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
 #define mk_pmd(page,prot)	pfn_pmd(page_to_pfn(page),prot)
 
-/* represent a notpresent pmd by zero, this is used by pmdp_invalidate */
+/* represent a notpresent pmd by faulting entry, this is used by pmdp_invalidate */
 static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 {
-	return __pmd(0);
+	return __pmd(pmd_val(pmd) & ~PMD_TYPE_MASK);
 }
 
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)

Signature · 1 line

2.1.0

Kirill A. Shutemov

2016-03-02 15:11 UTC #1 lore raw

PATCH 1/1 arm: mm: Fix definition of pmd_mknotpresent

Quoted 31 lines · Steve Capper

Currently pmd_mknotpresent will use a zero entry to respresent an invalidated pmd.
Unfortunately this definition clashes with pmd_none, thus it is possible for a race condition to occur if zap_pmd_range sees pmd_none whilst __split_huge_pmd_locked is running too with pmdp_invalidate just called.
This patch fixes the race condition by modifying pmd_mknotpresent to create non-zero faulting entries (as is done in other architectures), removing the ambiguity with pmd_none.
Fixes 8d9625070073 ("ARM: mm: Transparent huge page support for LPAE systems.")
Reported-by Kirill A. Shutemov <[email protected]>
Signed-off-by Steve Capper <[email protected]>
Acked-by Will Deacon <[email protected]>
---
This patch addresses an issue discussed at:
http://lkml.iu.edu/hypermail/linux/kernel/1602.3/01846.html
---
 arch/arm/include/asm/pgtable-3level.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
arch/arm/include/asm/pgtable-3level.h +0 -0
index dc46398..451b6e7 100644

arch/arm/include/asm/pgtable-3level.h PMD_BIT_FUNC(mkyoung, |= PMD_SECT_AF); · line 255

Quoted 9 lines

arch/arm/include/asm/pgtable-3level.h +2 -2

@@ -249,10 +249,10 @@ PMD_BIT_FUNC(mkyoung,   |= PMD_SECT_AF);
 #define pfn_pmd(pfn,prot)	(__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
 #define mk_pmd(page,prot)	pfn_pmd(page_to_pfn(page),prot)
 
-/* represent a notpresent pmd by zero, this is used by pmdp_invalidate */
+/* represent a notpresent pmd by faulting entry, this is used by pmdp_invalidate */
 static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 {
-	return __pmd(0);
+	return __pmd(pmd_val(pmd) & ~PMD_TYPE_MASK);

I'm confused. Wouldn't it still be present?

arch/arm/include/asm/pgtable.h:#define pmd_present(pmd) (pmd_val(pmd))

Shouldn't pmd_present() be re-defined as (pmd_val(pmd) & PMD_TYPE_MASK) or something?

Signature · 1 line

 Kirill A. Shutemov

Will Deacon

2016-03-02 15:55 UTC #2 lore raw

PATCH 1/1 arm: mm: Fix definition of pmd_mknotpresent

Quoted 44 lines · Kirill A. Shutemov

Quoted 31 lines · Steve Capper
Currently pmd_mknotpresent will use a zero entry to respresent an invalidated pmd.
Unfortunately this definition clashes with pmd_none, thus it is possible for a race condition to occur if zap_pmd_range sees pmd_none whilst __split_huge_pmd_locked is running too with pmdp_invalidate just called.
This patch fixes the race condition by modifying pmd_mknotpresent to create non-zero faulting entries (as is done in other architectures), removing the ambiguity with pmd_none.
Fixes 8d9625070073 ("ARM: mm: Transparent huge page support for LPAE systems.")
Reported-by Kirill A. Shutemov <[email protected]>
Signed-off-by Steve Capper <[email protected]>
Acked-by Will Deacon <[email protected]>
---
This patch addresses an issue discussed at:
http://lkml.iu.edu/hypermail/linux/kernel/1602.3/01846.html
---
 arch/arm/include/asm/pgtable-3level.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
arch/arm/include/asm/pgtable-3level.h +0 -0
index dc46398..451b6e7 100644
arch/arm/include/asm/pgtable-3level.h PMD_BIT_FUNC(mkyoung, |= PMD_SECT_AF); · line 255
Quoted 9 lines
arch/arm/include/asm/pgtable-3level.h +2 -2
@@ -249,10 +249,10 @@ PMD_BIT_FUNC(mkyoung,   |= PMD_SECT_AF);
 #define pfn_pmd(pfn,prot)	(__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
 #define mk_pmd(page,prot)	pfn_pmd(page_to_pfn(page),prot)
 
-/* represent a notpresent pmd by zero, this is used by pmdp_invalidate */
+/* represent a notpresent pmd by faulting entry, this is used by pmdp_invalidate */
 static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 {
-	return __pmd(0);
+	return __pmd(pmd_val(pmd) & ~PMD_TYPE_MASK);
I'm confused. Wouldn't it still be present?

Quoted 4 lines

arch/arm/include/asm/pgtable.h:#define pmd_present(pmd) (pmd_val(pmd))
Shouldn't pmd_present() be re-defined as (pmd_val(pmd) & PMD_TYPE_MASK) or something?

Hmm, we have ths same issue on arm64 in that case. Do we also need to handle PROT_NONE for pmds?

Will

Kirill A. Shutemov

2016-03-02 18:07 UTC #3 lore raw

PATCH 1/1 arm: mm: Fix definition of pmd_mknotpresent

Quoted 45 lines · Will Deacon

Quoted 44 lines · Kirill A. Shutemov
Quoted 31 lines · Steve Capper
Currently pmd_mknotpresent will use a zero entry to respresent an invalidated pmd.
Unfortunately this definition clashes with pmd_none, thus it is possible for a race condition to occur if zap_pmd_range sees pmd_none whilst __split_huge_pmd_locked is running too with pmdp_invalidate just called.
This patch fixes the race condition by modifying pmd_mknotpresent to create non-zero faulting entries (as is done in other architectures), removing the ambiguity with pmd_none.
Fixes 8d9625070073 ("ARM: mm: Transparent huge page support for LPAE systems.")
Reported-by Kirill A. Shutemov <[email protected]>
Signed-off-by Steve Capper <[email protected]>
Acked-by Will Deacon <[email protected]>
---
This patch addresses an issue discussed at:
http://lkml.iu.edu/hypermail/linux/kernel/1602.3/01846.html
---
 arch/arm/include/asm/pgtable-3level.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
arch/arm/include/asm/pgtable-3level.h +0 -0
index dc46398..451b6e7 100644
arch/arm/include/asm/pgtable-3level.h PMD_BIT_FUNC(mkyoung, |= PMD_SECT_AF); · line 255
Quoted 9 lines
arch/arm/include/asm/pgtable-3level.h +2 -2
@@ -249,10 +249,10 @@ PMD_BIT_FUNC(mkyoung,   |= PMD_SECT_AF);
 #define pfn_pmd(pfn,prot)	(__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
 #define mk_pmd(page,prot)	pfn_pmd(page_to_pfn(page),prot)
 
-/* represent a notpresent pmd by zero, this is used by pmdp_invalidate */
+/* represent a notpresent pmd by faulting entry, this is used by pmdp_invalidate */
 static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 {
-	return __pmd(0);
+	return __pmd(pmd_val(pmd) & ~PMD_TYPE_MASK);
I'm confused. Wouldn't it still be present?

Quoted 7 lines

Quoted 4 lines
arch/arm/include/asm/pgtable.h:#define pmd_present(pmd) (pmd_val(pmd))
Shouldn't pmd_present() be re-defined as (pmd_val(pmd) & PMD_TYPE_MASK) or something?
Hmm, we have ths same issue on arm64 in that case. Do we also need to handle PROT_NONE for pmds?

I think so.

There's no use-cases where it would matter at the moment as far as I can see. But if we would implement huge migration/swap entries, proper pmd_present() will be required.

Signature · 1 line

 Kirill A. Shutemov