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Thu, 29 Jun 2023 19:04:53 -0700 (PDT) Date: Thu, 29 Jun 2023 19:04:35 -0700 In-Reply-To: <20230630020436.1066016-1-surenb@google.com> Mime-Version: 1.0 References: <20230630020436.1066016-1-surenb@google.com> X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog Message-ID: <20230630020436.1066016-7-surenb@google.com> Subject: [PATCH v6 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 Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A20C8C000F X-Stat-Signature: 1yjzn3woswntnb63q9cnikykk63fr6qd X-Rspam-User: X-HE-Tag: 1688090694-282800 X-HE-Meta: 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 LsYUPLfI 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 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 Acked-by: Peter Xu --- fs/userfaultfd.c | 34 ++++++++++++++-------------------- include/linux/mm.h | 24 ++++++++++++++++++++++++ mm/memory.c | 9 --------- 3 files changed, 38 insertions(+), 29 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 7cecd49e078b..21a546eaf9f7 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(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; @@ -338,7 +335,7 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, pte_t ptent; bool ret = true; - mmap_assert_locked(mm); + assert_fault_locked(vmf); pgd = pgd_offset(mm, address); if (!pgd_present(*pgd)) @@ -440,7 +437,7 @@ 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(vmf); ctx = vma->vm_userfaultfd_ctx.ctx; if (!ctx) @@ -556,15 +553,12 @@ 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 54ab11214f4f..2794225b2d42 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; @@ -728,6 +739,14 @@ static inline void release_fault_lock(struct vm_fault *vmf) mmap_read_unlock(vmf->vma->vm_mm); } +static inline void assert_fault_locked(struct vm_fault *vmf) +{ + if (vmf->flags & FAULT_FLAG_VMA_LOCK) + vma_assert_locked(vmf->vma); + else + mmap_assert_locked(vmf->vma->vm_mm); +} + struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, unsigned long address); @@ -748,6 +767,11 @@ static inline void release_fault_lock(struct vm_fault *vmf) mmap_read_unlock(vmf->vma->vm_mm); } +static inline void assert_fault_locked(struct vm_fault *vmf) +{ + mmap_assert_locked(vmf->vma->vm_mm); +} + #endif /* CONFIG_PER_VMA_LOCK */ /* diff --git a/mm/memory.c b/mm/memory.c index bb0f68a73b0c..d9f36f9392a9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5407,15 +5407,6 @@ 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); -- 2.41.0.255.g8b1d071c50-goog