From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753740AbeD3OHu (ORCPT ); Mon, 30 Apr 2018 10:07:50 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:54902 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751949AbeD3OHs (ORCPT ); Mon, 30 Apr 2018 10:07:48 -0400 Subject: Re: [PATCH v10 06/25] mm: make pte_unmap_same compatible with SPF To: Minchan Kim 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 References: <1523975611-15978-1-git-send-email-ldufour@linux.vnet.ibm.com> <1523975611-15978-7-git-send-email-ldufour@linux.vnet.ibm.com> <20180423063157.GB114098@rodete-desktop-imager.corp.google.com> From: Laurent Dufour Date: Mon, 30 Apr 2018 16:07:30 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180423063157.GB114098@rodete-desktop-imager.corp.google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18043014-0040-0000-0000-000004347DF6 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18043014-0041-0000-0000-0000263893D0 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-30_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804300135 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/04/2018 08:31, Minchan Kim wrote: > 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. Late in the series, pte_spinlock() will check for the VMA's changes and may return 1. This will be then required to handle the 3 cases presented above. I can move this handling later in the series, but I wondering if this will make it more easier to read. > >> 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 >> >