[PATCH 0/2] Introduce PTE

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* [PATCH 0/2] Introduce PTE_WRITE for arm64
@ 2014-01-15 14:07 Steve Capper
  2014-01-15 14:07 ` [PATCH 1/2] arm64: mm: Remove PTE_BIT_FUNC macro Steve Capper
  2014-01-15 14:07 ` [PATCH 2/2] arm64: mm: Introduce PTE_WRITE Steve Capper
  0 siblings, 2 replies; 3+ messages in thread
From: Steve Capper @ 2014-01-15 14:07 UTC (permalink / raw)
  To: linux-arm-kernel

This series adds support for a separate PTE_WRITE bit, allowing one to
distinguish between writable clean ptes and read only ptes. At the
moment we have the following bit encodings:

                                PTE_DIRTY       PTE_RDONLY
!pte_dirty && !pte_write        0               1
!pte_dirty && pte_write         0               1
pte_dirty && !pte_write         1               1
pte_dirty && pte_write          1               0

One reason we need to add the distinction is to fix a problem with huge
pages, described here:
http://lists.infradead.org/pipermail/linux-arm-kernel/2013-November/215155.html

The patch in the link above attempts to address this issue by bypassing
set_pte_at in the huge page code, but it was decided that the lack of
distinction between writable clean ptes and read only ptes should be
addressed instead as it could likely lead to other issues that we've
not yet seen.

The first patch in the series expands out PTE_BIT_FUNC to make life
much easier for cscope and tags users. Whilst the second patch actually
introduces PTE_WRITE.

LPAE on ARM is also affected by this issue and will need a similar
patch.

Steve Capper (2):
  arm64: mm: Remove PTE_BIT_FUNC macro
  arm64: mm: Introduce PTE_WRITE

 arch/arm64/include/asm/pgtable.h | 93 +++++++++++++++++++++++++++-------------
 1 file changed, 63 insertions(+), 30 deletions(-)

-- 
1.8.1.4

^ permalink raw reply	[flat|nested] 3+ messages in thread

* [PATCH 1/2] arm64: mm: Remove PTE_BIT_FUNC macro
  2014-01-15 14:07 [PATCH 0/2] Introduce PTE_WRITE for arm64 Steve Capper
@ 2014-01-15 14:07 ` Steve Capper
  2014-01-15 14:07 ` [PATCH 2/2] arm64: mm: Introduce PTE_WRITE Steve Capper
  1 sibling, 0 replies; 3+ messages in thread
From: Steve Capper @ 2014-01-15 14:07 UTC (permalink / raw)
  To: linux-arm-kernel

Expand out the pte manipulation functions. This makes our life easier
when using things like tags and cscope.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/include/asm/pgtable.h | 51 ++++++++++++++++++++++++++++++++--------
 1 file changed, 41 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 7f2b60a..27c7839 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -146,16 +146,47 @@ extern struct page *empty_zero_page;
 #define pte_valid_user(pte) \
 	((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER))
 
-#define PTE_BIT_FUNC(fn,op) \
-static inline pte_t pte_##fn(pte_t pte) { pte_val(pte) op; return pte; }
-
-PTE_BIT_FUNC(wrprotect, |= PTE_RDONLY);
-PTE_BIT_FUNC(mkwrite,   &= ~PTE_RDONLY);
-PTE_BIT_FUNC(mkclean,   &= ~PTE_DIRTY);
-PTE_BIT_FUNC(mkdirty,   |= PTE_DIRTY);
-PTE_BIT_FUNC(mkold,     &= ~PTE_AF);
-PTE_BIT_FUNC(mkyoung,   |= PTE_AF);
-PTE_BIT_FUNC(mkspecial, |= PTE_SPECIAL);
+static inline pte_t pte_wrprotect(pte_t pte)
+{
+	pte_val(pte) |= PTE_RDONLY;
+	return pte;
+}
+
+static inline pte_t pte_mkwrite(pte_t pte)
+{
+	pte_val(pte) &= ~PTE_RDONLY;
+	return pte;
+}
+
+static inline pte_t pte_mkclean(pte_t pte)
+{
+	pte_val(pte) &= ~PTE_DIRTY;
+	return pte;
+}
+
+static inline pte_t pte_mkdirty(pte_t pte)
+{
+	pte_val(pte) |= PTE_DIRTY;
+	return pte;
+}
+
+static inline pte_t pte_mkold(pte_t pte)
+{
+	pte_val(pte) &= ~PTE_AF;
+	return pte;
+}
+
+static inline pte_t pte_mkyoung(pte_t pte)
+{
+	pte_val(pte) |= PTE_AF;
+	return pte;
+}
+
+static inline pte_t pte_mkspecial(pte_t pte)
+{
+	pte_val(pte) |= PTE_SPECIAL;
+	return pte;
+}
 
 static inline void set_pte(pte_t *ptep, pte_t pte)
 {
-- 
1.8.1.4

^ permalink raw reply related	[flat|nested] 3+ messages in thread

* [PATCH 2/2] arm64: mm: Introduce PTE_WRITE
  2014-01-15 14:07 [PATCH 0/2] Introduce PTE_WRITE for arm64 Steve Capper
  2014-01-15 14:07 ` [PATCH 1/2] arm64: mm: Remove PTE_BIT_FUNC macro Steve Capper
@ 2014-01-15 14:07 ` Steve Capper
  1 sibling, 0 replies; 3+ messages in thread
From: Steve Capper @ 2014-01-15 14:07 UTC (permalink / raw)
  To: linux-arm-kernel

We have the following means for encoding writable or dirty ptes:

                                PTE_DIRTY       PTE_RDONLY
!pte_dirty && !pte_write        0               1
!pte_dirty && pte_write         0               1
pte_dirty && !pte_write         1               1
pte_dirty && pte_write          1               0

So we can't distinguish between writable clean ptes and read only
ptes. This can cause problems with ptes being incorrectly flagged as
read only when they are writable but not dirty.

This patch introduces a new software bit PTE_WRITE which allows us to
correctly identify writable ptes. PTE_RDONLY is now only clear for
valid ptes where a page is both writable and dirty.

Signed-off-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/include/asm/pgtable.h | 48 +++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 23 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 27c7839..b524dcd 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -28,7 +28,7 @@
 #define PTE_FILE		(_AT(pteval_t, 1) << 2)	/* only when !pte_present() */
 #define PTE_DIRTY		(_AT(pteval_t, 1) << 55)
 #define PTE_SPECIAL		(_AT(pteval_t, 1) << 56)
-				/* bit 57 for PMD_SECT_SPLITTING */
+#define PTE_WRITE		(_AT(pteval_t, 1) << 57)
 #define PTE_PROT_NONE		(_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
 
 /*
@@ -67,15 +67,15 @@ extern pgprot_t pgprot_default;
 
 #define _MOD_PROT(p, b)		__pgprot_modify(p, 0, b)
 
-#define PAGE_NONE		__pgprot_modify(pgprot_default, PTE_TYPE_MASK, PTE_PROT_NONE | PTE_RDONLY | PTE_PXN | PTE_UXN)
-#define PAGE_SHARED		_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
-#define PAGE_SHARED_EXEC	_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
-#define PAGE_COPY		_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define PAGE_COPY_EXEC		_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define PAGE_READONLY		_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define PAGE_READONLY_EXEC	_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define PAGE_KERNEL		_MOD_PROT(pgprot_default, PTE_PXN | PTE_UXN | PTE_DIRTY)
-#define PAGE_KERNEL_EXEC	_MOD_PROT(pgprot_default, PTE_UXN | PTE_DIRTY)
+#define PAGE_NONE		__pgprot_modify(pgprot_default, PTE_TYPE_MASK, PTE_PROT_NONE | PTE_PXN | PTE_UXN)
+#define PAGE_SHARED		_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
+#define PAGE_SHARED_EXEC	_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
+#define PAGE_COPY		_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define PAGE_COPY_EXEC		_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
+#define PAGE_READONLY		_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define PAGE_READONLY_EXEC	_MOD_PROT(pgprot_default, PTE_USER | PTE_NG | PTE_PXN)
+#define PAGE_KERNEL		_MOD_PROT(pgprot_default, PTE_PXN | PTE_UXN | PTE_DIRTY | PTE_WRITE)
+#define PAGE_KERNEL_EXEC	_MOD_PROT(pgprot_default, PTE_UXN | PTE_DIRTY | PTE_WRITE)
 
 #define PAGE_HYP		_MOD_PROT(pgprot_default, PTE_HYP)
 #define PAGE_HYP_DEVICE		__pgprot(PROT_DEVICE_nGnRE | PTE_HYP)
@@ -83,13 +83,13 @@ extern pgprot_t pgprot_default;
 #define PAGE_S2			__pgprot_modify(pgprot_default, PTE_S2_MEMATTR_MASK, PTE_S2_MEMATTR(MT_S2_NORMAL) | PTE_S2_RDONLY)
 #define PAGE_S2_DEVICE		__pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_DEVICE_nGnRE) | PTE_S2_RDWR | PTE_UXN)
 
-#define __PAGE_NONE		__pgprot(((_PAGE_DEFAULT) & ~PTE_TYPE_MASK) | PTE_PROT_NONE | PTE_RDONLY | PTE_PXN | PTE_UXN)
-#define __PAGE_SHARED		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
-#define __PAGE_SHARED_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
-#define __PAGE_COPY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define __PAGE_COPY_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
-#define __PAGE_READONLY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_RDONLY)
-#define __PAGE_READONLY_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_RDONLY)
+#define __PAGE_NONE		__pgprot(((_PAGE_DEFAULT) & ~PTE_TYPE_MASK) | PTE_PROT_NONE | PTE_PXN | PTE_UXN)
+#define __PAGE_SHARED		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)
+#define __PAGE_SHARED_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_WRITE)
+#define __PAGE_COPY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define __PAGE_COPY_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
+#define __PAGE_READONLY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN)
+#define __PAGE_READONLY_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN)
 
 #endif /* __ASSEMBLY__ */
 
@@ -140,7 +140,7 @@ extern struct page *empty_zero_page;
 #define pte_dirty(pte)		(pte_val(pte) & PTE_DIRTY)
 #define pte_young(pte)		(pte_val(pte) & PTE_AF)
 #define pte_special(pte)	(pte_val(pte) & PTE_SPECIAL)
-#define pte_write(pte)		(!(pte_val(pte) & PTE_RDONLY))
+#define pte_write(pte)		(pte_val(pte) & PTE_WRITE)
 #define pte_exec(pte)		(!(pte_val(pte) & PTE_UXN))
 
 #define pte_valid_user(pte) \
@@ -148,13 +148,13 @@ extern struct page *empty_zero_page;
 
 static inline pte_t pte_wrprotect(pte_t pte)
 {
-	pte_val(pte) |= PTE_RDONLY;
+	pte_val(pte) &= ~PTE_WRITE;
 	return pte;
 }
 
 static inline pte_t pte_mkwrite(pte_t pte)
 {
-	pte_val(pte) &= ~PTE_RDONLY;
+	pte_val(pte) |= PTE_WRITE;
 	return pte;
 }
 
@@ -201,8 +201,10 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 	if (pte_valid_user(pte)) {
 		if (pte_exec(pte))
 			__sync_icache_dcache(pte, addr);
-		if (!pte_dirty(pte))
-			pte = pte_wrprotect(pte);
+		if (pte_dirty(pte) && pte_write(pte))
+			pte_val(pte) &= ~PTE_RDONLY;
+		else
+			pte_val(pte) |= PTE_RDONLY;
 	}
 
 	set_pte(ptep, pte);
@@ -376,7 +378,7 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
-			      PTE_PROT_NONE | PTE_VALID;
+			      PTE_PROT_NONE | PTE_VALID | PTE_WRITE;
 	pte_val(pte) = (pte_val(pte) & ~mask) | (pgprot_val(newprot) & mask);
 	return pte;
 }
-- 
1.8.1.4

^ permalink raw reply related	[flat|nested] 3+ messages in thread

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2014-01-15 14:07 [PATCH 0/2] Introduce PTE_WRITE for arm64 Steve Capper
2014-01-15 14:07 ` [PATCH 1/2] arm64: mm: Remove PTE_BIT_FUNC macro Steve Capper
2014-01-15 14:07 ` [PATCH 2/2] arm64: mm: Introduce PTE_WRITE Steve Capper

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