Some architectures support the accessed bit on non-leaf PMD entries (parents) in addition to leaf PTE entries (children) where pages are mapped, e.g., x86_64 sets the accessed bit on a parent when using it as part of linear-address translation [1]. Page table walkers who are interested in the accessed bit on children can take advantage of this: they do not need to search the children when the accessed bit is not set on a parent, given that they have previously cleared the accessed bit on this parent in addition to its children. [1]: Intel 64 and IA-32 Architectures Software Developer's Manual Volume 3 (October 2019), section 4.8 Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx> --- arch/Kconfig | 8 ++++++++ arch/x86/Kconfig | 1 + arch/x86/include/asm/pgtable.h | 2 +- arch/x86/mm/pgtable.c | 5 ++++- include/linux/pgtable.h | 4 ++-- 5 files changed, 16 insertions(+), 4 deletions(-) diff --git a/arch/Kconfig b/arch/Kconfig index 2bb30673d8e6..137446d17732 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -783,6 +783,14 @@ config HAVE_ARCH_TRANSPARENT_HUGEPAGE config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD bool +config HAVE_ARCH_PARENT_PMD_YOUNG + bool + help + Architectures that select this are able to set the accessed bit on + non-leaf PMD entries in addition to leaf PTE entries where pages are + mapped. For them, page table walkers that clear the accessed bit may + stop at non-leaf PMD entries when they do not see the accessed bit. + config HAVE_ARCH_HUGE_VMAP bool diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 2792879d398e..b5972eb82337 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -163,6 +163,7 @@ config X86 select HAVE_ARCH_TRACEHOOK select HAVE_ARCH_TRANSPARENT_HUGEPAGE select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64 + select HAVE_ARCH_PARENT_PMD_YOUNG if X86_64 select HAVE_ARCH_USERFAULTFD_WP if X86_64 && USERFAULTFD select HAVE_ARCH_VMAP_STACK if X86_64 select HAVE_ARCH_WITHIN_STACK_FRAMES diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index a02c67291cfc..a6b5cfe1fc5a 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -846,7 +846,7 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd) static inline int pmd_bad(pmd_t pmd) { - return (pmd_flags(pmd) & ~_PAGE_USER) != _KERNPG_TABLE; + return ((pmd_flags(pmd) | _PAGE_ACCESSED) & ~_PAGE_USER) != _KERNPG_TABLE; } static inline unsigned long pages_to_mb(unsigned long npg) diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index f6a9e2e36642..1c27e6f43f80 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -550,7 +550,7 @@ int ptep_test_and_clear_young(struct vm_area_struct *vma, return ret; } -#ifdef CONFIG_TRANSPARENT_HUGEPAGE +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG) int pmdp_test_and_clear_young(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmdp) { @@ -562,6 +562,9 @@ int pmdp_test_and_clear_young(struct vm_area_struct *vma, return ret; } +#endif + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE int pudp_test_and_clear_young(struct vm_area_struct *vma, unsigned long addr, pud_t *pudp) { diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 5e772392a379..08dd9b8c055a 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -193,7 +193,7 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma, #endif #ifndef __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG -#ifdef CONFIG_TRANSPARENT_HUGEPAGE +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG) static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp) @@ -214,7 +214,7 @@ static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma, BUILD_BUG(); return 0; } -#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ +#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG */ #endif #ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH -- 2.31.0.rc2.261.g7f71774620-goog