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Subject[PATCH 5.9 034/152] arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect()
Date
From: Will Deacon <will@kernel.org>

commit ff1712f953e27f0b0718762ec17d0adb15c9fd0b upstream.

With hardware dirty bit management, calling pte_wrprotect() on a writable,
dirty PTE will lose the dirty state and return a read-only, clean entry.

Move the logic from ptep_set_wrprotect() into pte_wrprotect() to ensure that
the dirty bit is preserved for writable entries, as this is required for
soft-dirty bit management if we enable it in the future.

Cc: <stable@vger.kernel.org>
Fixes: 2f4b829c625e ("arm64: Add support for hardware updates of the access and dirty pte bits")
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20201120143557.6715-3-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++-------------
1 file changed, 14 insertions(+), 13 deletions(-)

--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -146,13 +146,6 @@ static inline pte_t set_pte_bit(pte_t pt
return pte;
}

-static inline pte_t pte_wrprotect(pte_t pte)
-{
- pte = clear_pte_bit(pte, __pgprot(PTE_WRITE));
- pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
- return pte;
-}
-
static inline pte_t pte_mkwrite(pte_t pte)
{
pte = set_pte_bit(pte, __pgprot(PTE_WRITE));
@@ -178,6 +171,20 @@ static inline pte_t pte_mkdirty(pte_t pt
return pte;
}

+static inline pte_t pte_wrprotect(pte_t pte)
+{
+ /*
+ * If hardware-dirty (PTE_WRITE/DBM bit set and PTE_RDONLY
+ * clear), set the PTE_DIRTY bit.
+ */
+ if (pte_hw_dirty(pte))
+ pte = pte_mkdirty(pte);
+
+ pte = clear_pte_bit(pte, __pgprot(PTE_WRITE));
+ pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
+ return pte;
+}
+
static inline pte_t pte_mkold(pte_t pte)
{
return clear_pte_bit(pte, __pgprot(PTE_AF));
@@ -799,12 +806,6 @@ static inline void ptep_set_wrprotect(st
pte = READ_ONCE(*ptep);
do {
old_pte = pte;
- /*
- * If hardware-dirty (PTE_WRITE/DBM bit set and PTE_RDONLY
- * clear), set the PTE_DIRTY bit.
- */
- if (pte_hw_dirty(pte))
- pte = pte_mkdirty(pte);
pte = pte_wrprotect(pte);
pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
pte_val(old_pte), pte_val(pte));

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