Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932280Ab2KMRXp (ORCPT ); Tue, 13 Nov 2012 12:23:45 -0500 Received: from mail-ee0-f46.google.com ([74.125.83.46]:37723 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755237Ab2KMROi (ORCPT ); Tue, 13 Nov 2012 12:14:38 -0500 From: Ingo Molnar To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Paul Turner , Lee Schermerhorn , Christoph Lameter , Rik van Riel , Mel Gorman , Andrew Morton , Andrea Arcangeli , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , Michel Lespinasse Subject: [PATCH 01/31] mm/generic: Only flush the local TLB in ptep_set_access_flags() Date: Tue, 13 Nov 2012 18:13:24 +0100 Message-Id: <1352826834-11774-2-git-send-email-mingo@kernel.org> X-Mailer: git-send-email 1.7.11.7 In-Reply-To: <1352826834-11774-1-git-send-email-mingo@kernel.org> References: <1352826834-11774-1-git-send-email-mingo@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2715 Lines: 68 From: Rik van Riel The function ptep_set_access_flags() is only ever used to upgrade access permissions to a page - i.e. they make it less restrictive. That means the only negative side effect of not flushing remote TLBs in this function is that other CPUs may incur spurious page faults, if they happen to access the same address, and still have a PTE with the old permissions cached in their TLB caches. Having another CPU maybe incur a spurious page fault is faster than always incurring the cost of a remote TLB flush, so replace the remote TLB flush with a purely local one. This should be safe on every architecture that correctly implements flush_tlb_fix_spurious_fault() to actually invalidate the local TLB entry that caused a page fault, as well as on architectures where the hardware invalidates TLB entries that cause page faults. In the unlikely event that you are hitting what appears to be an infinite loop of page faults, and 'git bisect' took you to this changeset, your architecture needs to implement flush_tlb_fix_spurious_fault() to actually flush the TLB entry. Signed-off-by: Rik van Riel Acked-by: Linus Torvalds Acked-by: Peter Zijlstra Cc: Andrew Morton Cc: Michel Lespinasse [ Changelog massage. ] Signed-off-by: Ingo Molnar --- mm/pgtable-generic.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c index e642627..d8397da 100644 --- a/mm/pgtable-generic.c +++ b/mm/pgtable-generic.c @@ -12,8 +12,8 @@ #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS /* - * Only sets the access flags (dirty, accessed, and - * writable). Furthermore, we know it always gets set to a "more + * Only sets the access flags (dirty, accessed), as well as write + * permission. Furthermore, we know it always gets set to a "more * permissive" setting, which allows most architectures to optimize * this. We return whether the PTE actually changed, which in turn * instructs the caller to do things like update__mmu_cache. This @@ -27,7 +27,7 @@ int ptep_set_access_flags(struct vm_area_struct *vma, int changed = !pte_same(*ptep, entry); if (changed) { set_pte_at(vma->vm_mm, address, ptep, entry); - flush_tlb_page(vma, address); + flush_tlb_fix_spurious_fault(vma, address); } return changed; } -- 1.7.11.7 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/