x86/mm: Reduce tlb flushes from ptep_set_access_flags()
Commit-ID: d8769ca9a6272795acf650698abe29d8ed149888 Gitweb: http://git.kernel.org/tip/d8769ca9a6272795acf650698abe29d8ed149888 Author: Rik van Riel <[email protected]> AuthorDate: Tue, 9 Oct 2012 15:31:34 +0200 Committer: Ingo Molnar <[email protected]> CommitDate: Fri, 12 Oct 2012 12:07:15 +0200
x86/mm: Reduce tlb flushes from ptep_set_access_flags()
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 files changed, 16 insertions(+), 1 deletions(-)
arch/x86/mm/pgtable.c +16 -1
@@ -306,11 +306,26 @@ int ptep_set_access_flags(struct vm_area_struct *vma, 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;