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um: Avoid marking pages with "changed protection"

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[ Upstream commit 8892d8545f ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Anton Ivanov 2018-12-05 12:37:41 +00:00 • committed by Greg Kroah-Hartman
commit 1e480ee6c0
1 changed files with 8 additions and 1 deletions
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9
arch/um/include/asm/pgtable.h
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@ -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));
}