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[70.31.26.132]) by smtp.gmail.com with ESMTPSA id s21-20020a05620a0bd500b006fa4ac86bfbsm202359qki.55.2022.12.16.07.52.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Dec 2022 07:52:32 -0800 (PST) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: David Hildenbrand , John Hubbard , Muchun Song , Mike Kravetz , Nadav Amit , Andrea Arcangeli , Rik van Riel , peterx@redhat.com, Miaohe Lin , Jann Horn , James Houghton , Andrew Morton Subject: [PATCH v4 9/9] mm/hugetlb: Introduce hugetlb_walk() Date: Fri, 16 Dec 2022 10:52:29 -0500 Message-Id: <20221216155229.2043750-1-peterx@redhat.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221216155100.2043537-1-peterx@redhat.com> References: <20221216155100.2043537-1-peterx@redhat.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1752386595770817410?= X-GMAIL-MSGID: =?utf-8?q?1752386595770817410?= huge_pte_offset() is the main walker function for hugetlb pgtables. The name is not really representing what it does, though. Instead of renaming it, introduce a wrapper function called hugetlb_walk() which will use huge_pte_offset() inside. Assert on the locks when walking the pgtable. Note, the vma lock assertion will be a no-op for private mappings. Document the last special case in the page_vma_mapped_walk() path where we don't need any more lock to call hugetlb_walk(). Taking vma lock there is not needed because either: (1) potential callers of hugetlb pvmw holds i_mmap_rwsem already (from one rmap_walk()), or (2) the caller will not walk a hugetlb vma at all so the hugetlb code path not reachable (e.g. in ksm or uprobe paths). It's slightly implicit for future page_vma_mapped_walk() callers on that lock requirement. But anyway, when one day this rule breaks, one will get a straightforward warning in hugetlb_walk() with lockdep, then there'll be a way out. Reviewed-by: Mike Kravetz Reviewed-by: John Hubbard Signed-off-by: Peter Xu Reviewed-by: David Hildenbrand --- fs/hugetlbfs/inode.c | 4 +--- fs/userfaultfd.c | 6 ++---- include/linux/hugetlb.h | 37 +++++++++++++++++++++++++++++++++++++ mm/hugetlb.c | 31 +++++++++++++------------------ mm/page_vma_mapped.c | 9 ++++++--- mm/pagewalk.c | 4 +--- 6 files changed, 60 insertions(+), 31 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index fdb16246f46e..48f1a8ad2243 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -388,9 +388,7 @@ static bool hugetlb_vma_maps_page(struct vm_area_struct *vma, { pte_t *ptep, pte; - ptep = huge_pte_offset(vma->vm_mm, addr, - huge_page_size(hstate_vma(vma))); - + ptep = hugetlb_walk(vma, addr, huge_page_size(hstate_vma(vma))); if (!ptep) return false; diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 887e20472051..4e27ff526873 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -237,14 +237,12 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, unsigned long flags, unsigned long reason) { - struct mm_struct *mm = ctx->mm; pte_t *ptep, pte; bool ret = true; - mmap_assert_locked(mm); - - ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma)); + mmap_assert_locked(ctx->mm); + ptep = hugetlb_walk(vma, address, vma_mmu_pagesize(vma)); if (!ptep) goto out; diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index d755e2a7c0db..b6b10101bea7 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -2,6 +2,7 @@ #ifndef _LINUX_HUGETLB_H #define _LINUX_HUGETLB_H +#include #include #include #include @@ -196,6 +197,11 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma, * huge_pte_offset(): Walk the hugetlb pgtable until the last level PTE. * Returns the pte_t* if found, or NULL if the address is not mapped. * + * IMPORTANT: we should normally not directly call this function, instead + * this is only a common interface to implement arch-specific + * walker. Please use hugetlb_walk() instead, because that will attempt to + * verify the locking for you. + * * Since this function will walk all the pgtable pages (including not only * high-level pgtable page, but also PUD entry that can be unshared * concurrently for VM_SHARED), the caller of this function should be @@ -1229,4 +1235,35 @@ bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr); #define flush_hugetlb_tlb_range(vma, addr, end) flush_tlb_range(vma, addr, end) #endif +static inline bool __vma_shareable_lock(struct vm_area_struct *vma) +{ + return (vma->vm_flags & VM_MAYSHARE) && vma->vm_private_data; +} + +/* + * Safe version of huge_pte_offset() to check the locks. See comments + * above huge_pte_offset(). + */ +static inline pte_t * +hugetlb_walk(struct vm_area_struct *vma, unsigned long addr, unsigned long sz) +{ +#if defined(CONFIG_HUGETLB_PAGE) && \ + defined(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) && defined(CONFIG_LOCKDEP) + struct hugetlb_vma_lock *vma_lock = vma->vm_private_data; + + /* + * If pmd sharing possible, locking needed to safely walk the + * hugetlb pgtables. More information can be found at the comment + * above huge_pte_offset() in the same file. + * + * NOTE: lockdep_is_held() is only defined with CONFIG_LOCKDEP. + */ + if (__vma_shareable_lock(vma)) + WARN_ON_ONCE(!lockdep_is_held(&vma_lock->rw_sema) && + !lockdep_is_held( + &vma->vm_file->f_mapping->i_mmap_rwsem)); +#endif + return huge_pte_offset(vma->vm_mm, addr, sz); +} + #endif /* _LINUX_HUGETLB_H */ diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 33fe73e1e589..21dc37ff0896 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -258,11 +258,6 @@ static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma) /* * hugetlb vma_lock helper routines */ -static bool __vma_shareable_lock(struct vm_area_struct *vma) -{ - return vma->vm_flags & VM_MAYSHARE && vma->vm_private_data; -} - void hugetlb_vma_lock_read(struct vm_area_struct *vma) { if (__vma_shareable_lock(vma)) { @@ -4959,7 +4954,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, } else { /* * For shared mappings the vma lock must be held before - * calling huge_pte_offset in the src vma. Otherwise, the + * calling hugetlb_walk() in the src vma. Otherwise, the * returned ptep could go away if part of a shared pmd and * another thread calls huge_pmd_unshare. */ @@ -4969,7 +4964,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, last_addr_mask = hugetlb_mask_last_page(h); for (addr = src_vma->vm_start; addr < src_vma->vm_end; addr += sz) { spinlock_t *src_ptl, *dst_ptl; - src_pte = huge_pte_offset(src, addr, sz); + src_pte = hugetlb_walk(src_vma, addr, sz); if (!src_pte) { addr |= last_addr_mask; continue; @@ -5176,7 +5171,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, hugetlb_vma_lock_write(vma); i_mmap_lock_write(mapping); for (; old_addr < old_end; old_addr += sz, new_addr += sz) { - src_pte = huge_pte_offset(mm, old_addr, sz); + src_pte = hugetlb_walk(vma, old_addr, sz); if (!src_pte) { old_addr |= last_addr_mask; new_addr |= last_addr_mask; @@ -5239,7 +5234,7 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct last_addr_mask = hugetlb_mask_last_page(h); address = start; for (; address < end; address += sz) { - ptep = huge_pte_offset(mm, address, sz); + ptep = hugetlb_walk(vma, address, sz); if (!ptep) { address |= last_addr_mask; continue; @@ -5552,7 +5547,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma, mutex_lock(&hugetlb_fault_mutex_table[hash]); hugetlb_vma_lock_read(vma); spin_lock(ptl); - ptep = huge_pte_offset(mm, haddr, huge_page_size(h)); + ptep = hugetlb_walk(vma, haddr, huge_page_size(h)); if (likely(ptep && pte_same(huge_ptep_get(ptep), pte))) goto retry_avoidcopy; @@ -5590,7 +5585,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma, * before the page tables are altered */ spin_lock(ptl); - ptep = huge_pte_offset(mm, haddr, huge_page_size(h)); + ptep = hugetlb_walk(vma, haddr, huge_page_size(h)); if (likely(ptep && pte_same(huge_ptep_get(ptep), pte))) { /* Break COW or unshare */ huge_ptep_clear_flush(vma, haddr, ptep); @@ -6376,7 +6371,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma, return NULL; hugetlb_vma_lock_read(vma); - pte = huge_pte_offset(mm, haddr, huge_page_size(h)); + pte = hugetlb_walk(vma, haddr, huge_page_size(h)); if (!pte) goto out_unlock; @@ -6441,8 +6436,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, * * Note that page table lock is not held when pte is null. */ - pte = huge_pte_offset(mm, vaddr & huge_page_mask(h), - huge_page_size(h)); + pte = hugetlb_walk(vma, vaddr & huge_page_mask(h), + huge_page_size(h)); if (pte) ptl = huge_pte_lock(h, mm, pte); absent = !pte || huge_pte_none(huge_ptep_get(pte)); @@ -6633,7 +6628,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, last_addr_mask = hugetlb_mask_last_page(h); for (; address < end; address += psize) { spinlock_t *ptl; - ptep = huge_pte_offset(mm, address, psize); + ptep = hugetlb_walk(vma, address, psize); if (!ptep) { address |= last_addr_mask; continue; @@ -7040,8 +7035,8 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma, saddr = page_table_shareable(svma, vma, addr, idx); if (saddr) { - spte = huge_pte_offset(svma->vm_mm, saddr, - vma_mmu_pagesize(svma)); + spte = hugetlb_walk(svma, saddr, + vma_mmu_pagesize(svma)); if (spte) { get_page(virt_to_page(spte)); break; @@ -7358,7 +7353,7 @@ void hugetlb_unshare_all_pmds(struct vm_area_struct *vma) hugetlb_vma_lock_write(vma); i_mmap_lock_write(vma->vm_file->f_mapping); for (address = start; address < end; address += PUD_SIZE) { - ptep = huge_pte_offset(mm, address, sz); + ptep = hugetlb_walk(vma, address, sz); if (!ptep) continue; ptl = huge_pte_lock(h, mm, ptep); diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index 93e13fc17d3c..f3729b23dd0e 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -168,9 +168,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) /* The only possible mapping was handled on last iteration */ if (pvmw->pte) return not_found(pvmw); - - /* when pud is not present, pte will be NULL */ - pvmw->pte = huge_pte_offset(mm, pvmw->address, size); + /* + * All callers that get here will already hold the + * i_mmap_rwsem. Therefore, no additional locks need to be + * taken before calling hugetlb_walk(). + */ + pvmw->pte = hugetlb_walk(vma, pvmw->address, size); if (!pvmw->pte) return false; diff --git a/mm/pagewalk.c b/mm/pagewalk.c index d98564a7be57..cb23f8a15c13 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -305,13 +305,11 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end, hugetlb_vma_lock_read(vma); do { next = hugetlb_entry_end(h, addr, end); - pte = huge_pte_offset(walk->mm, addr & hmask, sz); - + pte = hugetlb_walk(vma, addr & hmask, sz); if (pte) err = ops->hugetlb_entry(pte, hmask, addr, next, walk); else if (ops->pte_hole) err = ops->pte_hole(addr, next, -1, walk); - if (err) break; } while (addr = next, addr != end);