Commit-ID: d8769ca9a6272795acf650698abe29d8ed149888 Gitweb: http://git.kernel.org/tip/d8769ca9a6272795acf650698abe29d8ed149888 Author: Rik van Riel <r...@redhat.com> AuthorDate: Tue, 9 Oct 2012 15:31:34 +0200 Committer: Ingo Molnar <mi...@kernel.org> 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 <r...@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijls...@chello.nl> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Andrew Morton <a...@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijls...@chello.nl> Link: http://lkml.kernel.org/n/tip-zb7fqnz7byn1xmaei148p...@git.kernel.org Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/mm/pgtable.c | 17 ++++++++++++++++- 1 files changed, 16 insertions(+), 1 deletions(-) diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 8573b83..fc82cf1 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
