From: Rik van Riel <[email protected]> If ptep_set_access_flags() is invoked to upgrade access permissions on a PTE, there is no security or data integrity reason to do a remote TLB flush.
Lazily letting another CPU incur a spurious page fault occasionally is (much!) cheaper than aggressively flushing everybody else's TLB. Signed-off-by: Rik van Riel <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Peter Zijlstra <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/mm/pgtable.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) Index: tip/arch/x86/mm/pgtable.c =================================================================== --- tip.orig/arch/x86/mm/pgtable.c +++ tip/arch/x86/mm/pgtable.c @@ -306,11 +306,26 @@ int ptep_set_access_flags(struct vm_area pte_t entry, int dirty) { int changed = !pte_same(*ptep, entry); + /* + * If the page used to be inaccessible (_PAGE_PROTNONE), or + * this call upgrades the access permissions on the same page, + * it is safe to skip the remote TLB flush. + */ + bool flush_remote = false; + if (!pte_accessible(*ptep)) + flush_remote = false; + else if (pte_pfn(*ptep) != pte_pfn(entry) || + (pte_write(*ptep) && !pte_write(entry)) || + (pte_exec(*ptep) && !pte_exec(entry))) + flush_remote = true; if (changed && dirty) { *ptep = entry; pte_update_defer(vma->vm_mm, address, ptep); - flush_tlb_page(vma, address); + if (flush_remote) + flush_tlb_page(vma, address); + else + __flush_tlb_one(address); } return changed; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
