From cef23d9db6b76732d9b0933cb162358a6a1f43d7 Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Tue, 6 Nov 2012 09:56:01 +0000 Subject: mm,generic: only flush the local TLB in ptep_set_access_flags The function ptep_set_access_flags is only ever used to upgrade access permissions to a page. That means the only negative side effect of not flushing remote TLBs 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. 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 Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Cc: Michel Lespinasse Cc: Ingo Molnar --- mm/pgtable-generic.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'mm/pgtable-generic.c') diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c index e642627da6b..d8397da42fe 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; } -- cgit v1.2.3-70-g09d2 From 8d1acce4537c4e2f5889ed9ba9b8eddb80d99820 Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Tue, 9 Oct 2012 15:31:59 +0200 Subject: mm: Only flush the TLB when clearing an accessible pte If ptep_clear_flush() is called to clear a page table entry that is accessible anyway by the CPU, eg. a _PAGE_PROTNONE page table entry, there is no need to flush the TLB on remote CPUs. Signed-off-by: Rik van Riel Signed-off-by: Peter Zijlstra Cc: Linus Torvalds Cc: Andrew Morton Link: http://lkml.kernel.org/n/tip-vm3rkzevahelwhejx5uwm8ex@git.kernel.org Signed-off-by: Ingo Molnar --- mm/pgtable-generic.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'mm/pgtable-generic.c') diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c index d8397da42fe..0c8323fe6c8 100644 --- a/mm/pgtable-generic.c +++ b/mm/pgtable-generic.c @@ -88,7 +88,8 @@ pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long address, { pte_t pte; pte = ptep_get_and_clear((vma)->vm_mm, address, ptep); - flush_tlb_page(vma, address); + if (pte_accessible(pte)) + flush_tlb_page(vma, address); return pte; } #endif -- cgit v1.2.3-70-g09d2