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Wed, 28 Jun 2023 00:18:18 -0700 (PDT) Date: Wed, 28 Jun 2023 00:18:00 -0700 In-Reply-To: <20230628071800.544800-1-surenb@google.com> Mime-Version: 1.0 References: <20230628071800.544800-1-surenb@google.com> X-Mailer: git-send-email 2.41.0.162.gfafddb0af9-goog Message-ID: <20230628071800.544800-7-surenb@google.com> Subject: [PATCH v4 6/6] mm: handle userfaults under VMA lock From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: willy@infradead.org, hannes@cmpxchg.org, mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz, minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com, lstoakes@gmail.com, hdanton@sina.com, apopple@nvidia.com, peterx@redhat.com, ying.huang@intel.com, david@redhat.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, pasha.tatashin@soleen.com, surenb@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 5F72E160004 X-Stat-Signature: xzcd4edush9dcc81fm3were7753eygto X-HE-Tag: 1687936699-671940 X-HE-Meta: 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 1aUwXFAs Xzp2viqFWgCW/SHqU5y5v3rzKDmHOZ6PN4SWigouq/V1R/lo3cJmLAUoScHvNGqfvnZvHcuXMFfhWFW9eBmXaVtNM/QEhyPlcqBGAmAnpQxZyipFmznQGx2K7K6CsmDSItO2wLX05BzF3/YafmFSSpLbUdL/TOQCaFPKF5W9pIM6LlqnMu5ngSU207frOL0JObwchNm1qGtrW4iHTX2Im0QbJv/UdvGnZKkYAz+GsPJ6vVK436Fnqwng3eqzyCt3mpbUN/dSAUXqojm+4K2OsMc/yAFQSgmBxTn0HmfKvRqxcMgJHmpu0iU+gLrI0QruSzEjLaLg7h6gs2FuaK9J5hun0OMCj8inpdgoTWAfoqjhiKcdoyk0Y9/w8daocAv3t0WfaqJ01FhmV+xe6LPoIxfQzJxHCroPtvZC3bziQ/dPWyXV/bBB1mGFUAppJCRwxyrbDZt55doO51HZrlv4WiF/79VZrf3llJCLI7r36xwQwVCSLzpqOkjq3bpmCsymJxt0lfk4/6RdCvYywpmoVdl9v29Ymy6pyHWi1j7NJeeidnQhI5JYfdKQ7TnvcfJ4/MzL7nv6fQkbbaT1JhqXDtDVvbp96Wfs80BZPJXyCvrc7Ge4= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Enable handle_userfault to operate under VMA lock by releasing VMA lock instead of mmap_lock and retrying. Note that FAULT_FLAG_RETRY_NOWAIT should never be used when handling faults under per-VMA lock protection because that would break the assumption that lock is dropped on retry. Signed-off-by: Suren Baghdasaryan --- fs/userfaultfd.c | 39 ++++++++++++++++++--------------------- include/linux/mm.h | 39 +++++++++++++++++++++++++++++++++++++++ mm/filemap.c | 8 -------- mm/memory.c | 9 --------- 4 files changed, 57 insertions(+), 38 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 4e800bb7d2ab..d019e7df6f15 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -277,17 +277,16 @@ static inline struct uffd_msg userfault_msg(unsigned long address, * hugepmd ranges. */ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, - struct vm_area_struct *vma, - unsigned long address, - unsigned long flags, - unsigned long reason) + struct vm_fault *vmf, + unsigned long reason) { + struct vm_area_struct *vma = vmf->vma; pte_t *ptep, pte; bool ret = true; - mmap_assert_locked(ctx->mm); + assert_fault_locked(ctx->mm, vmf); - ptep = hugetlb_walk(vma, address, vma_mmu_pagesize(vma)); + ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma)); if (!ptep) goto out; @@ -308,10 +307,8 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, } #else static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, - struct vm_area_struct *vma, - unsigned long address, - unsigned long flags, - unsigned long reason) + struct vm_fault *vmf, + unsigned long reason) { return false; /* should never get here */ } @@ -325,11 +322,11 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, * threads. */ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, - unsigned long address, - unsigned long flags, + struct vm_fault *vmf, unsigned long reason) { struct mm_struct *mm = ctx->mm; + unsigned long address = vmf->address; pgd_t *pgd; p4d_t *p4d; pud_t *pud; @@ -337,7 +334,7 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, pte_t *pte; bool ret = true; - mmap_assert_locked(mm); + assert_fault_locked(mm, vmf); pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) @@ -445,7 +442,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) * Coredumping runs without mmap_lock so we can only check that * the mmap_lock is held, if PF_DUMPCORE was not set. */ - mmap_assert_locked(mm); + assert_fault_locked(mm, vmf); ctx = vma->vm_userfaultfd_ctx.ctx; if (!ctx) @@ -522,8 +519,11 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) * and wait. */ ret = VM_FAULT_RETRY; - if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) + if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) { + /* Per-VMA lock is expected to be dropped on VM_FAULT_RETRY */ + BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT); goto out; + } /* take the reference before dropping the mmap_lock */ userfaultfd_ctx_get(ctx); @@ -561,15 +561,12 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) spin_unlock_irq(&ctx->fault_pending_wqh.lock); if (!is_vm_hugetlb_page(vma)) - must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags, - reason); + must_wait = userfaultfd_must_wait(ctx, vmf, reason); else - must_wait = userfaultfd_huge_must_wait(ctx, vma, - vmf->address, - vmf->flags, reason); + must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason); if (is_vm_hugetlb_page(vma)) hugetlb_vma_unlock_read(vma); - mmap_read_unlock(mm); + release_fault_lock(vmf); if (likely(must_wait && !READ_ONCE(ctx->released))) { wake_up_poll(&ctx->fd_wqh, EPOLLIN); diff --git a/include/linux/mm.h b/include/linux/mm.h index fec149585985..70bb2f923e33 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -705,6 +705,17 @@ static inline bool vma_try_start_write(struct vm_area_struct *vma) return true; } +static inline void vma_assert_locked(struct vm_area_struct *vma) +{ + int mm_lock_seq; + + if (__is_vma_write_locked(vma, &mm_lock_seq)) + return; + + lockdep_assert_held(&vma->vm_lock->lock); + VM_BUG_ON_VMA(!rwsem_is_locked(&vma->vm_lock->lock), vma); +} + static inline void vma_assert_write_locked(struct vm_area_struct *vma) { int mm_lock_seq; @@ -723,6 +734,23 @@ static inline void vma_mark_detached(struct vm_area_struct *vma, bool detached) struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, unsigned long address); +static inline +void assert_fault_locked(struct mm_struct *mm, struct vm_fault *vmf) +{ + if (vmf->flags & FAULT_FLAG_VMA_LOCK) + vma_assert_locked(vmf->vma); + else + mmap_assert_locked(mm); +} + +static inline void release_fault_lock(struct vm_fault *vmf) +{ + if (vmf->flags & FAULT_FLAG_VMA_LOCK) + vma_end_read(vmf->vma); + else + mmap_read_unlock(vmf->vma->vm_mm); +} + #else /* CONFIG_PER_VMA_LOCK */ static inline void vma_init_lock(struct vm_area_struct *vma) {} @@ -736,6 +764,17 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma) {} static inline void vma_mark_detached(struct vm_area_struct *vma, bool detached) {} +static inline +void assert_fault_locked(struct mm_struct *mm, struct vm_fault *vmf) +{ + mmap_assert_locked(mm); +} + +static inline void release_fault_lock(struct vm_fault *vmf) +{ + mmap_read_unlock(vmf->vma->vm_mm); +} + #endif /* CONFIG_PER_VMA_LOCK */ /* diff --git a/mm/filemap.c b/mm/filemap.c index 7ee078e1a0d2..d4d8f474e0c5 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1699,14 +1699,6 @@ static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait) return ret; } -static void release_fault_lock(struct vm_fault *vmf) -{ - if (vmf->flags & FAULT_FLAG_VMA_LOCK) - vma_end_read(vmf->vma); - else - mmap_read_unlock(vmf->vma->vm_mm); -} - /* * Return values: * 0 - folio is locked. diff --git a/mm/memory.c b/mm/memory.c index 76c7907e7286..c6c759922f39 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5294,15 +5294,6 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, if (!vma_start_read(vma)) goto inval; - /* - * Due to the possibility of userfault handler dropping mmap_lock, avoid - * it for now and fall back to page fault handling under mmap_lock. - */ - if (userfaultfd_armed(vma)) { - vma_end_read(vma); - goto inval; - } - /* Check since vm_start/vm_end might change before we lock the VMA */ if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { vma_end_read(vma);