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authorAnton Ivanov <anton.ivanov@cambridgegreys.com>2018-12-05 12:37:41 +0000
committerRichard Weinberger <richard@nod.at>2018-12-27 22:48:34 +0100
commit8892d8545f2d0342b9c550defbfb165db237044b (patch)
tree0b48c4df948da4a350321e4d8067cf243562a37b /arch/um/include
parent38e3cbd9b82c815006c505ad2995013a61af143e (diff)
um: Avoid marking pages with "changed protection"
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 <anton.ivanov@cambridgegreys.com> Signed-off-by: Richard Weinberger <richard@nod.at>
Diffstat (limited to 'arch/um/include')
-rw-r--r--arch/um/include/asm/pgtable.h9
1 files changed, 8 insertions, 1 deletions
diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h
index 7485398d0737..9c04562310b3 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));
}