From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752224AbeDWGcK (ORCPT ); Mon, 23 Apr 2018 02:32:10 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:42529 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750852AbeDWGcI (ORCPT ); Mon, 23 Apr 2018 02:32:08 -0400 X-Google-Smtp-Source: AIpwx4/s7WK1s+WipW2b0Hl3CNOvg0TFNSQ7gKlwgRKMANoBj1yXBe9P7bHw5p3JkaotkhN6grD13g== Date: Mon, 23 Apr 2018 15:31:57 +0900 From: Minchan Kim To: Laurent Dufour Cc: akpm@linux-foundation.org, mhocko@kernel.org, peterz@infradead.org, kirill@shutemov.name, ak@linux.intel.com, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com, Daniel Jordan , David Rientjes , Jerome Glisse , Ganesh Mahendran , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, paulmck@linux.vnet.ibm.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org Subject: Re: [PATCH v10 06/25] mm: make pte_unmap_same compatible with SPF Message-ID: <20180423063157.GB114098@rodete-desktop-imager.corp.google.com> References: <1523975611-15978-1-git-send-email-ldufour@linux.vnet.ibm.com> <1523975611-15978-7-git-send-email-ldufour@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1523975611-15978-7-git-send-email-ldufour@linux.vnet.ibm.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 17, 2018 at 04:33:12PM +0200, Laurent Dufour wrote: > pte_unmap_same() is making the assumption that the page table are still > around because the mmap_sem is held. > This is no more the case when running a speculative page fault and > additional check must be made to ensure that the final page table are still > there. > > This is now done by calling pte_spinlock() to check for the VMA's > consistency while locking for the page tables. > > This is requiring passing a vm_fault structure to pte_unmap_same() which is > containing all the needed parameters. > > As pte_spinlock() may fail in the case of a speculative page fault, if the > VMA has been touched in our back, pte_unmap_same() should now return 3 > cases : > 1. pte are the same (0) > 2. pte are different (VM_FAULT_PTNOTSAME) > 3. a VMA's changes has been detected (VM_FAULT_RETRY) > > The case 2 is handled by the introduction of a new VM_FAULT flag named > VM_FAULT_PTNOTSAME which is then trapped in cow_user_page(). I don't see such logic in this patch. Maybe you introduces it later? If so, please comment on it. Or just return 0 in case of 2 without introducing VM_FAULT_PTNOTSAME. > If VM_FAULT_RETRY is returned, it is passed up to the callers to retry the > page fault while holding the mmap_sem. > > Acked-by: David Rientjes > Signed-off-by: Laurent Dufour > --- > include/linux/mm.h | 1 + > mm/memory.c | 39 ++++++++++++++++++++++++++++----------- > 2 files changed, 29 insertions(+), 11 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 4d1aff80669c..714da99d77a3 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1208,6 +1208,7 @@ static inline void clear_page_pfmemalloc(struct page *page) > #define VM_FAULT_NEEDDSYNC 0x2000 /* ->fault did not modify page tables > * and needs fsync() to complete (for > * synchronous page faults in DAX) */ > +#define VM_FAULT_PTNOTSAME 0x4000 /* Page table entries have changed */ > > #define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \ > VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \ > diff --git a/mm/memory.c b/mm/memory.c > index 0b9a51f80e0e..f86efcb8e268 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2309,21 +2309,29 @@ static inline bool pte_map_lock(struct vm_fault *vmf) > * parts, do_swap_page must check under lock before unmapping the pte and > * proceeding (but do_wp_page is only called after already making such a check; > * and do_anonymous_page can safely check later on). > + * > + * pte_unmap_same() returns: > + * 0 if the PTE are the same > + * VM_FAULT_PTNOTSAME if the PTE are different > + * VM_FAULT_RETRY if the VMA has changed in our back during > + * a speculative page fault handling. > */ > -static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd, > - pte_t *page_table, pte_t orig_pte) > +static inline int pte_unmap_same(struct vm_fault *vmf) > { > - int same = 1; > + int ret = 0; > + > #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT) > if (sizeof(pte_t) > sizeof(unsigned long)) { > - spinlock_t *ptl = pte_lockptr(mm, pmd); > - spin_lock(ptl); > - same = pte_same(*page_table, orig_pte); > - spin_unlock(ptl); > + if (pte_spinlock(vmf)) { > + if (!pte_same(*vmf->pte, vmf->orig_pte)) > + ret = VM_FAULT_PTNOTSAME; > + spin_unlock(vmf->ptl); > + } else > + ret = VM_FAULT_RETRY; > } > #endif > - pte_unmap(page_table); > - return same; > + pte_unmap(vmf->pte); > + return ret; > } > > static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma) > @@ -2912,10 +2920,19 @@ int do_swap_page(struct vm_fault *vmf) > pte_t pte; > int locked; > int exclusive = 0; > - int ret = 0; > + int ret; > > - if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte)) > + ret = pte_unmap_same(vmf); > + if (ret) { > + /* > + * If pte != orig_pte, this means another thread did the > + * swap operation in our back. > + * So nothing else to do. > + */ > + if (ret == VM_FAULT_PTNOTSAME) > + ret = 0; > goto out; > + } > > entry = pte_to_swp_entry(vmf->orig_pte); > if (unlikely(non_swap_entry(entry))) { > -- > 2.7.4 >