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Message-ID: <20230630020436.1066016-7-surenb@google.com>
Date: Thu, 29 Jun 2023 19:04:35 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: willy@...radead.org, hannes@...xchg.org, mhocko@...e.com,
josef@...icpanda.com, jack@...e.cz, ldufour@...ux.ibm.com,
laurent.dufour@...ibm.com, michel@...pinasse.org,
liam.howlett@...cle.com, jglisse@...gle.com, vbabka@...e.cz,
minchan@...gle.com, dave@...olabs.net, punit.agrawal@...edance.com,
lstoakes@...il.com, hdanton@...a.com, apopple@...dia.com,
peterx@...hat.com, ying.huang@...el.com, david@...hat.com,
yuzhao@...gle.com, dhowells@...hat.com, hughd@...gle.com,
viro@...iv.linux.org.uk, brauner@...nel.org,
pasha.tatashin@...een.com, surenb@...gle.com, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...roid.com
Subject: [PATCH v6 6/6] mm: handle userfaults under VMA lock
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 <surenb@...gle.com>
Acked-by: Peter Xu <peterx@...hat.com>
---
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
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