Messages in this thread Patch in this message | | | From | Nadav Amit <> | Subject | [RFC PATCH 12/14] x86/tlb: no flush on PTE change from RW->RO when PTE is clean | Date | Mon, 18 Jul 2022 05:02:10 -0700 |
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From: Nadav Amit <namit@vmware.com>
On x86 it is possible to skip a TLB flush when a RW entry become RO and the PTE is clean. Add logic to detect this case and skip the flush.
Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Hildenbrand <david@redhat.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: Nadav Amit <namit@vmware.com> --- arch/x86/include/asm/tlbflush.h | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index 4f98735ab07a..58c95e36b098 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -271,8 +271,9 @@ static inline enum pte_flush_type pte_flags_flush_type(unsigned long oldflags, * dirty/access bit if needed without a fault. */ const pteval_t flush_on_clear = _PAGE_DIRTY | _PAGE_PRESENT | - _PAGE_ACCESSED | _PAGE_RW; + _PAGE_ACCESSED; const pteval_t flush_on_set = _PAGE_NX; + const pteval_t flush_on_special = _PAGE_RW; const pteval_t flush_on_set_relaxed = _PAGE_RW; const pteval_t flush_on_clear_relaxed = _PAGE_NX; const pteval_t software_flags = _PAGE_SOFTW1 | _PAGE_SOFTW2 | @@ -302,6 +303,17 @@ static inline enum pte_flush_type pte_flags_flush_type(unsigned long oldflags, if (diff & oldflags & flush_on_clear) return PTE_FLUSH_STRICT; + /* + * Did any of the 'flush_on_set' flags was set between 'oldflags' and + * 'newflags'? + */ + if (diff & newflags & flush_on_set) + return PTE_FLUSH_STRICT; + + /* On RW->RO, a flush is needed if the old entry is dirty */ + if ((diff & oldflags & _PAGE_RW) && (oldflags & _PAGE_DIRTY)) + return PTE_FLUSH_STRICT; + /* Flush on modified flags. */ if (diff & flush_on_change) return PTE_FLUSH_STRICT; @@ -314,7 +326,7 @@ static inline enum pte_flush_type pte_flags_flush_type(unsigned long oldflags, /* Ensure there are no flags that were left behind */ if (IS_ENABLED(CONFIG_DEBUG_VM) && - (diff & ~(flush_on_clear | flush_on_set | + (diff & ~(flush_on_clear | flush_on_set | flush_on_special | software_flags | flush_on_change))) { VM_WARN_ON_ONCE(1); return PTE_FLUSH_STRICT; -- 2.25.1
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