From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752289Ab2LCUpj (ORCPT ); Mon, 3 Dec 2012 15:45:39 -0500 Received: from mail-pa0-f46.google.com ([209.85.220.46]:37852 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751279Ab2LCUpi (ORCPT ); Mon, 3 Dec 2012 15:45:38 -0500 From: David Daney To: linux-mips@linux-mips.org, Ralf Baechle , linux-kernel@vger.kernel.org Cc: Hillf Danton , David Daney Subject: [PATCH] MIPS: Avoid Machine Check by flushing entire page range in huge_ptep_set_access_flags(). Date: Mon, 3 Dec 2012 12:44:26 -0800 Message-Id: <1354567466-23571-1-git-send-email-ddaney.cavm@gmail.com> X-Mailer: git-send-email 1.7.11.7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: David Daney Problem: 1) Huge page mapping of anonymous memory is initially invalid. Will be faulted in by copy-on-write mechanism. 2) Userspace attempts store at the end of the huge mapping. 3) TLB Refill exception handler fill TLB with a normal (4K sized) invalid page at the end of the huge mapping virtual address range. 4) Userspace restarted, and re-attempts the store at the end of the huge mapping. 5) Page from #3 is invalid, we get a fault and go to the hugepage fault handler. This tries to map a huge page and calls huge_ptep_set_access_flags() to install the mapping. 6) We just call the generic ptep_set_access_flags() to set up the page tables, but the flush there assumes a normal (4K sized) page and only tries to flush the first part of the huge page virtual address out of the TLB, since the existing entry from step #3 doesn't conflict, nothing is flushed. 7) We attempt to load the mapping into the TLB, but because it conflicts with the entry from step #3, we get a Machine Check exception. The fix: Flush the entire rage covered by the huge page in huge_ptep_set_access_flags(), and remove the optimization in local_flush_tlb_range() so that the flush actually does the correct thing. Signed-off-by: David Daney --- arch/mips/include/asm/hugetlb.h | 12 +++++++++++- arch/mips/mm/tlb-r4k.c | 18 ++++-------------- 2 files changed, 15 insertions(+), 15 deletions(-) diff --git a/arch/mips/include/asm/hugetlb.h b/arch/mips/include/asm/hugetlb.h index 58d3688..68670b1 100644 --- a/arch/mips/include/asm/hugetlb.h +++ b/arch/mips/include/asm/hugetlb.h @@ -95,7 +95,17 @@ static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma, pte_t *ptep, pte_t pte, int dirty) { - return ptep_set_access_flags(vma, addr, ptep, pte, dirty); + int changed = !pte_same(*ptep, pte); + + if (changed) { + set_pte_at(vma->vm_mm, addr, ptep, pte); + /* + * There could be some standard sized pages in there, + * get them all. + */ + flush_tlb_range(vma, addr, addr + HPAGE_SIZE); + } + return changed; } static inline pte_t huge_ptep_get(pte_t *ptep) diff --git a/arch/mips/mm/tlb-r4k.c b/arch/mips/mm/tlb-r4k.c index d2572cb..1df4d2f 100644 --- a/arch/mips/mm/tlb-r4k.c +++ b/arch/mips/mm/tlb-r4k.c @@ -120,18 +120,11 @@ void local_flush_tlb_range(struct vm_area_struct *vma, unsigned long start, if (cpu_context(cpu, mm) != 0) { unsigned long size, flags; - int huge = is_vm_hugetlb_page(vma); ENTER_CRITICAL(flags); - if (huge) { - start = round_down(start, HPAGE_SIZE); - end = round_up(end, HPAGE_SIZE); - size = (end - start) >> HPAGE_SHIFT; - } else { - start = round_down(start, PAGE_SIZE << 1); - end = round_up(end, PAGE_SIZE << 1); - size = (end - start) >> (PAGE_SHIFT + 1); - } + start = round_down(start, PAGE_SIZE << 1); + end = round_up(end, PAGE_SIZE << 1); + size = (end - start) >> (PAGE_SHIFT + 1); if (size <= current_cpu_data.tlbsize/2) { int oldpid = read_c0_entryhi(); int newpid = cpu_asid(cpu, mm); @@ -140,10 +133,7 @@ void local_flush_tlb_range(struct vm_area_struct *vma, unsigned long start, int idx; write_c0_entryhi(start | newpid); - if (huge) - start += HPAGE_SIZE; - else - start += (PAGE_SIZE << 1); + start += (PAGE_SIZE << 1); mtc0_tlbw_hazard(); tlb_probe(); tlb_probe_hazard(); -- 1.7.11.7