From 64c26841b34957ef8f33f7a9e8663aeee59c3ded Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Wed, 5 Jul 2017 10:59:42 +0100 Subject: arm64: Ignore hardware dirty bit updates in ptep_set_wrprotect() ptep_set_wrprotect() is only called on CoW mappings which are private (!VM_SHARED) with the pte either read-only (!PTE_WRITE && PTE_RDONLY) or writable and software-dirty (PTE_WRITE && !PTE_RDONLY && PTE_DIRTY). There is no race with the hardware update of the dirty state: clearing of PTE_RDONLY when PTE_WRITE (a.k.a. PTE_DBM) is set. This patch removes the code setting the software PTE_DIRTY bit in ptep_set_wrprotect() as superfluous. A VM_WARN_ONCE is introduced in case the above logic is wrong or the core mm code changes its use of ptep_set_wrprotect(). Reviewed-by: Will Deacon Acked-by: Steve Capper Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/pgtable.h | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) (limited to 'arch/arm64/include/asm/pgtable.h') diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index a04bfb869a80..0117cbcd62d4 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -634,23 +634,28 @@ static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm, #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ /* - * ptep_set_wrprotect - mark read-only while trasferring potential hardware - * dirty status (PTE_DBM && !PTE_RDONLY) to the software PTE_DIRTY bit. + * ptep_set_wrprotect - mark read-only while preserving the hardware update of + * the Access Flag. */ #define __HAVE_ARCH_PTEP_SET_WRPROTECT static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long address, pte_t *ptep) { pte_t old_pte, pte; + /* + * ptep_set_wrprotect() is only called on CoW mappings which are + * private (!VM_SHARED) with the pte either read-only (!PTE_WRITE && + * PTE_RDONLY) or writable and software-dirty (PTE_WRITE && + * !PTE_RDONLY && PTE_DIRTY); see is_cow_mapping() and + * protection_map[]. There is no race with the hardware update of the + * dirty state: clearing of PTE_RDONLY when PTE_WRITE (a.k.a. PTE_DBM) + * is set. + */ + VM_WARN_ONCE(pte_write(*ptep) && !pte_dirty(*ptep), + "%s: potential race with hardware DBM", __func__); 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)); -- cgit v1.2.3-59-g8ed1b