From e8f13f32f436e3fae2b43a433ec5c677e0e2f5f9 Mon Sep 17 00:00:00 2001 From: Anton Ivanov Date: Wed, 5 Dec 2018 12:37:41 +0000 Subject: [PATCH] um: Avoid marking pages with "changed protection" [ Upstream commit 8892d8545f2d0342b9c550defbfb165db237044b ] Changing protection is a very high cost operation in UML because in addition to an extra syscall it also interrupts mmap merge sequences generated by the tlb. While the condition is not particularly common it is worth avoiding. Signed-off-by: Anton Ivanov Signed-off-by: Richard Weinberger Signed-off-by: Sasha Levin --- arch/um/include/asm/pgtable.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h index 7485398..9c04562 100644 --- a/arch/um/include/asm/pgtable.h +++ b/arch/um/include/asm/pgtable.h @@ -197,12 +197,17 @@ static inline pte_t pte_mkold(pte_t pte) static inline pte_t pte_wrprotect(pte_t pte) { - pte_clear_bits(pte, _PAGE_RW); + if (likely(pte_get_bits(pte, _PAGE_RW))) + pte_clear_bits(pte, _PAGE_RW); + else + return pte; return(pte_mknewprot(pte)); } static inline pte_t pte_mkread(pte_t pte) { + if (unlikely(pte_get_bits(pte, _PAGE_USER))) + return pte; pte_set_bits(pte, _PAGE_USER); return(pte_mknewprot(pte)); } @@ -221,6 +226,8 @@ static inline pte_t pte_mkyoung(pte_t pte) static inline pte_t pte_mkwrite(pte_t pte) { + if (unlikely(pte_get_bits(pte, _PAGE_RW))) + return pte; pte_set_bits(pte, _PAGE_RW); return(pte_mknewprot(pte)); } -- 2.7.4