diff options
| author | Nadav Amit | 2022-05-09 18:20:50 -0700 |
|---|---|---|
| committer | Andrew Morton | 2022-05-13 07:20:05 -0700 |
| commit | 4f83145721f362c2f4d312edc4755269a2069488 (patch) | |
| tree | 4a13cb87519b0bd3659d91f6f3a19df4575d4f96 /arch | |
| parent | c9fe66560bf2dc7d109754414e309888cb8c9ba9 (diff) | |
mm: avoid unnecessary flush on change_huge_pmd()
Calls to change_protection_range() on THP can trigger, at least on x86,
two TLB flushes for one page: one immediately, when pmdp_invalidate() is
called by change_huge_pmd(), and then another one later (that can be
batched) when change_protection_range() finishes.
The first TLB flush is only necessary to prevent the dirty bit (and with a
lesser importance the access bit) from changing while the PTE is modified.
However, this is not necessary as the x86 CPUs set the dirty-bit
atomically with an additional check that the PTE is (still) present. One
caveat is Intel's Knights Landing that has a bug and does not do so.
Leverage this behavior to eliminate the unnecessary TLB flush in
change_huge_pmd(). Introduce a new arch specific pmdp_invalidate_ad()
that only invalidates the access and dirty bit from further changes.
Link: https://lkml.kernel.org/r/20220401180821.1986781-4-namit@vmware.com
Signed-off-by: Nadav Amit <namit@vmware.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Nick Piggin <npiggin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/include/asm/pgtable.h | 5 | ||||
| -rw-r--r-- | arch/x86/mm/pgtable.c | 10 |
2 files changed, 15 insertions, 0 deletions
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 1e09519af143..0821f87d495f 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1168,6 +1168,11 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, } } #endif + +#define __HAVE_ARCH_PMDP_INVALIDATE_AD +extern pmd_t pmdp_invalidate_ad(struct vm_area_struct *vma, + unsigned long address, pmd_t *pmdp); + /* * Page table pages are page-aligned. The lower half of the top * level is used for userspace and the top half for the kernel. diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 3481b35cb4ec..f16059e9a85e 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -608,6 +608,16 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma, return young; } + +pmd_t pmdp_invalidate_ad(struct vm_area_struct *vma, unsigned long address, + pmd_t *pmdp) +{ + /* + * No flush is necessary. Once an invalid PTE is established, the PTE's + * access and dirty bits cannot be updated. + */ + return pmdp_establish(vma, address, pmdp, pmd_mkinvalid(*pmdp)); +} #endif /** |