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Shutemov" , Davidlohr Bueso , Prakash Sangappa , James Houghton , Mina Almasry , Pasha Tatashin , Axel Rasmussen , Ray Fucillo , Andrew Morton , Mike Kravetz Subject: [PATCH 1/3] hugetlb: fix vma lock handling during split vma and range unmapping Date: Tue, 4 Oct 2022 18:17:05 -0700 Message-Id: <20221005011707.514612-2-mike.kravetz@oracle.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221005011707.514612-1-mike.kravetz@oracle.com> References: <20221005011707.514612-1-mike.kravetz@oracle.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: MW4PR03CA0308.namprd03.prod.outlook.com (2603:10b6:303:dd::13) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY5PR10MB4196:EE_|SN7PR10MB6286:EE_ X-MS-Office365-Filtering-Correlation-Id: f0d77006-0151-4d51-c31a-08daa66f5601 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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text/plain; charset="utf-8" The hugetlb vma lock hangs off the vm_private_data field and is specific to the vma. When vm_area_dup() is called as part of vma splitting, the vma lock pointer is copied to the new vma. This will result in issues such as double freeing of the structure. Update the hugetlb open vm_ops to allocate a new vma lock for the new vma. The routine __unmap_hugepage_range_final unconditionally unset VM_MAYSHARE to prevent subsequent pmd sharing. hugetlb_vma_lock_free attempted to anticipate this by checking both VM_MAYSHARE and VM_SHARED. However, if only VM_MAYSHARE was set we would miss the free. With the introduction of the vma lock, a vma can not participate in pmd sharing if vm_private_data is NULL. Instead of clearing VM_MAYSHARE in __unmap_hugepage_range_final, free the vma lock to prevent sharing. Also, update the sharing code to make sure vma lock is indeed a condition for pmd sharing. hugetlb_vma_lock_free can then key off VM_MAYSHARE and not miss any vmas. Fixes: "hugetlb: add vma based lock for pmd sharing" Signed-off-by: Mike Kravetz --- mm/hugetlb.c | 43 +++++++++++++++++++++++++++---------------- mm/memory.c | 4 ---- 2 files changed, 27 insertions(+), 20 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 4443e87e814b..0129d371800c 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4612,7 +4612,14 @@ static void hugetlb_vm_op_open(struct vm_area_struct= *vma) kref_get(&resv->refs); } =20 - hugetlb_vma_lock_alloc(vma); + /* + * vma_lock structure for sharable mappings is vma specific. + * Clear old pointer (if copied via vm_area_dup) and create new. + */ + if (vma->vm_flags & VM_MAYSHARE) { + vma->vm_private_data =3D NULL; + hugetlb_vma_lock_alloc(vma); + } } =20 static void hugetlb_vm_op_close(struct vm_area_struct *vma) @@ -5168,19 +5175,23 @@ void __unmap_hugepage_range_final(struct mmu_gather= *tlb, unsigned long end, struct page *ref_page, zap_flags_t zap_flags) { + hugetlb_vma_lock_write(vma); + i_mmap_lock_write(vma->vm_file->f_mapping); + __unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags); =20 /* - * Clear this flag so that x86's huge_pmd_share page_table_shareable - * test will fail on a vma being torn down, and not grab a page table - * on its way out. We're lucky that the flag has such an appropriate - * name, and can in fact be safely cleared here. We could clear it - * before the __unmap_hugepage_range above, but all that's necessary - * is to clear it before releasing the i_mmap_rwsem. This works - * because in the context this is called, the VMA is about to be - * destroyed and the i_mmap_rwsem is held. + * Unlock and free the vma lock before releasing i_mmap_rwsem. When + * the vma_lock is freed, this makes the vma ineligible for pmd + * sharing. And, i_mmap_rwsem is required to set up pmd sharing. + * This is important as page tables for this unmapped range will + * be asynchrously deleted. If the page tables are shared, there + * will be issues when accessed by someone else. */ - vma->vm_flags &=3D ~VM_MAYSHARE; + hugetlb_vma_unlock_write(vma); + hugetlb_vma_lock_free(vma); + + i_mmap_unlock_write(vma->vm_file->f_mapping); } =20 void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start, @@ -6730,10 +6741,13 @@ static unsigned long page_table_shareable(struct vm= _area_struct *svma, /* * match the virtual addresses, permission and the alignment of the * page table page. + * + * Also, vma_lock (vm_private_data) is required for sharing. */ if (pmd_index(addr) !=3D pmd_index(saddr) || vm_flags !=3D svm_flags || - !range_in_vma(svma, sbase, s_end)) + !range_in_vma(svma, sbase, s_end) || + !svma->vm_private_data) return 0; =20 return saddr; @@ -6883,12 +6897,9 @@ void hugetlb_vma_lock_release(struct kref *kref) static void hugetlb_vma_lock_free(struct vm_area_struct *vma) { /* - * Only present in sharable vmas. See comment in - * __unmap_hugepage_range_final about how VM_SHARED could - * be set without VM_MAYSHARE. As a result, we need to - * check if either is set in the free path. + * Only present in sharable vmas. */ - if (!vma || !(vma->vm_flags & (VM_MAYSHARE | VM_SHARED))) + if (!vma || !__vma_shareable_flags_pmd(vma)) return; =20 if (vma->vm_private_data) { diff --git a/mm/memory.c b/mm/memory.c index 1b994a55f176..81cc75e71888 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1685,12 +1685,8 @@ static void unmap_single_vma(struct mmu_gather *tlb, if (vma->vm_file) { zap_flags_t zap_flags =3D details ? details->zap_flags : 0; - hugetlb_vma_lock_write(vma); - i_mmap_lock_write(vma->vm_file->f_mapping); __unmap_hugepage_range_final(tlb, vma, start, end, NULL, zap_flags); - i_mmap_unlock_write(vma->vm_file->f_mapping); - hugetlb_vma_unlock_write(vma); } } else unmap_page_range(tlb, vma, start, end, details); --=20 2.37.3 From nobody Mon Apr 6 18:07:55 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AA6A3C433FE for ; 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Wed, 5 Oct 2022 01:17:17 +0000 From: Mike Kravetz To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Muchun Song , Miaohe Lin , David Hildenbrand , Sven Schnelle , Michal Hocko , Peter Xu , Naoya Horiguchi , "Aneesh Kumar K . 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Shutemov" , Davidlohr Bueso , Prakash Sangappa , James Houghton , Mina Almasry , Pasha Tatashin , Axel Rasmussen , Ray Fucillo , Andrew Morton , Mike Kravetz Subject: [PATCH 2/3] hugetlb: take hugetlb vma_lock when clearing vma_lock->vma pointer Date: Tue, 4 Oct 2022 18:17:06 -0700 Message-Id: <20221005011707.514612-3-mike.kravetz@oracle.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221005011707.514612-1-mike.kravetz@oracle.com> References: <20221005011707.514612-1-mike.kravetz@oracle.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: MW4PR04CA0325.namprd04.prod.outlook.com (2603:10b6:303:82::30) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY5PR10MB4196:EE_|SN7PR10MB6286:EE_ X-MS-Office365-Filtering-Correlation-Id: 438385be-dde8-4d48-73a6-08daa66f579b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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text/plain; charset="utf-8" hugetlb file truncation/hole punch code may need to back out and take locks in order in the routine hugetlb_unmap_file_folio(). This code could race with vma freeing as pointed out in [1] and result in accessing a stale vma pointer. To address this, take the vma_lock when clearing the vma_lock->vma pointer. [1] https://lore.kernel.org/linux-mm/01f10195-7088-4462-6def-909549c75ef4@h= uawei.com/ Fixes: "hugetlb: use new vma_lock for pmd sharing synchronization" Signed-off-by: Mike Kravetz Reviewed-by: Miaohe Lin --- mm/hugetlb.c | 38 ++++++++++++++++++++++++++++---------- 1 file changed, 28 insertions(+), 10 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 0129d371800c..388a32b089bd 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -93,6 +93,7 @@ struct mutex *hugetlb_fault_mutex_table ____cacheline_ali= gned_in_smp; static int hugetlb_acct_memory(struct hstate *h, long delta); static void hugetlb_vma_lock_free(struct vm_area_struct *vma); static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma); +static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma); =20 static inline bool subpool_is_free(struct hugepage_subpool *spool) { @@ -5188,8 +5189,7 @@ void __unmap_hugepage_range_final(struct mmu_gather *= tlb, * be asynchrously deleted. If the page tables are shared, there * will be issues when accessed by someone else. */ - hugetlb_vma_unlock_write(vma); - hugetlb_vma_lock_free(vma); + __hugetlb_vma_unlock_write_free(vma); =20 i_mmap_unlock_write(vma->vm_file->f_mapping); } @@ -6894,6 +6894,30 @@ void hugetlb_vma_lock_release(struct kref *kref) kfree(vma_lock); } =20 +void __hugetlb_vma_unlock_write_put(struct hugetlb_vma_lock *vma_lock) +{ + struct vm_area_struct *vma =3D vma_lock->vma; + + /* + * vma_lock structure may or not be released as a result of put, + * it certainly will no longer be attached to vma so clear pointer. + * Semaphore synchronizes access to vma_lock->vma field. + */ + vma_lock->vma =3D NULL; + vma->vm_private_data =3D NULL; + up_write(&vma_lock->rw_sema); + kref_put(&vma_lock->refs, hugetlb_vma_lock_release); +} + +void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma) +{ + if (__vma_shareable_flags_pmd(vma)) { + struct hugetlb_vma_lock *vma_lock =3D vma->vm_private_data; + + __hugetlb_vma_unlock_write_put(vma_lock); + } +} + static void hugetlb_vma_lock_free(struct vm_area_struct *vma) { /* @@ -6905,14 +6929,8 @@ static void hugetlb_vma_lock_free(struct vm_area_str= uct *vma) if (vma->vm_private_data) { struct hugetlb_vma_lock *vma_lock =3D vma->vm_private_data; =20 - /* - * vma_lock structure may or not be released, but it - * certainly will no longer be attached to vma so clear - * pointer. - */ - vma_lock->vma =3D NULL; - kref_put(&vma_lock->refs, hugetlb_vma_lock_release); - vma->vm_private_data =3D NULL; + down_write(&vma_lock->rw_sema); + __hugetlb_vma_unlock_write_put(vma_lock); } } =20 --=20 2.37.3 From nobody Mon Apr 6 18:07:55 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AFF33C433FE for ; Wed, 5 Oct 2022 01:18:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229702AbiJEBSL (ORCPT ); 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text/plain; charset="utf-8" The hugetlb vma lock was originally designed to synchronize pmd sharing. As such, it was only necessary to allocate the lock for vmas that were capable of pmd sharing. Later in the development cycle, it was discovered that it could also be used to simplify fault/truncation races as described in [1]. However, a subsequent change to allocate the lock for all vmas that use the page cache was never made. A fault/truncation race could leave pages in a file past i_size until the file is removed. Remove the previous restriction and allocate lock for all VM_MAYSHARE vmas. Warn in the unlikely event of allocation failure. Fixes: "hugetlb: clean up code checking for fault/truncation races" Signed-off-by: Mike Kravetz [1] https://lore.kernel.org/lkml/Yxiv0SkMkZ0JWGGp@monkey/#t Reviewed-by: Miaohe Lin --- mm/hugetlb.c | 50 +++++++++++++++----------------------------------- 1 file changed, 15 insertions(+), 35 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 388a32b089bd..593aac995911 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6753,10 +6753,11 @@ static unsigned long page_table_shareable(struct vm= _area_struct *svma, return saddr; } =20 -static bool __vma_aligned_range_pmd_shareable(struct vm_area_struct *vma, - unsigned long start, unsigned long end, - bool check_vma_lock) +bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr) { + unsigned long start =3D addr & PUD_MASK; + unsigned long end =3D start + PUD_SIZE; + #ifdef CONFIG_USERFAULTFD if (uffd_disable_huge_pmd_share(vma)) return false; @@ -6766,38 +6767,13 @@ static bool __vma_aligned_range_pmd_shareable(struc= t vm_area_struct *vma, */ if (!(vma->vm_flags & VM_MAYSHARE)) return false; - if (check_vma_lock && !vma->vm_private_data) + if (!vma->vm_private_data) /* vma lock required for sharing */ return false; if (!range_in_vma(vma, start, end)) return false; return true; } =20 -static bool vma_pmd_shareable(struct vm_area_struct *vma) -{ - unsigned long start =3D ALIGN(vma->vm_start, PUD_SIZE), - end =3D ALIGN_DOWN(vma->vm_end, PUD_SIZE); - - if (start >=3D end) - return false; - - return __vma_aligned_range_pmd_shareable(vma, start, end, false); -} - -static bool vma_addr_pmd_shareable(struct vm_area_struct *vma, - unsigned long addr) -{ - unsigned long start =3D addr & PUD_MASK; - unsigned long end =3D start + PUD_SIZE; - - return __vma_aligned_range_pmd_shareable(vma, start, end, true); -} - -bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr) -{ - return vma_addr_pmd_shareable(vma, addr); -} - /* * Determine if start,end range within vma could be mapped by shared pmd. * If yes, adjust start and end to cover range associated with possible @@ -6946,17 +6922,21 @@ static void hugetlb_vma_lock_alloc(struct vm_area_s= truct *vma) if (vma->vm_private_data) return; =20 - /* Check size/alignment for pmd sharing possible */ - if (!vma_pmd_shareable(vma)) - return; - vma_lock =3D kmalloc(sizeof(*vma_lock), GFP_KERNEL); - if (!vma_lock) + if (!vma_lock) { /* * If we can not allocate structure, then vma can not - * participate in pmd sharing. + * participate in pmd sharing. This is only a possible + * performance enhancement and memory saving issue. + * However, the lock is also used to synchronize page + * faults with truncation. If the lock is not present, + * unlikely races could leave pages in a file past i_size + * until the file is removed. Warn in the unlikely case of + * allocation failure. */ + pr_warn_once("HugeTLB: unable to allocate vma specific lock\n"); return; + } =20 kref_init(&vma_lock->refs); init_rwsem(&vma_lock->rw_sema); --=20 2.37.3