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mm: handle userfaults under VMA lock

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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.

[surenb@google.com: fix a lockdep issue in vma_assert_write_locked]
  Link: https://lkml.kernel.org/r/20230712195652.969194-1-surenb@google.com
Link: https://lkml.kernel.org/r/20230630211957.1341547-7-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Hillf Danton <hdanton@sina.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michel Lespinasse <michel@lespinasse.org>
Cc: Minchan Kim <minchan@google.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Suren Baghdasaryan 2023-06-30 14:19:57 -07:00 committed by Andrew Morton
parent 1235ccd05b
commit 29a22b9e08
3 changed files with 35 additions and 28 deletions
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34
fs/userfaultfd.c
View file

@ -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);

20
include/linux/mm.h
View file

@ -679,6 +679,7 @@ static inline void vma_end_read(struct vm_area_struct *vma)
rcu_read_unlock();
}
/* WARNING! Can only be used if mmap_lock is expected to be write-locked */
static bool __is_vma_write_locked(struct vm_area_struct *vma, int *mm_lock_seq)
{
mmap_assert_write_locked(vma->vm_mm);
@ -721,6 +722,12 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma)
VM_BUG_ON_VMA(!__is_vma_write_locked(vma, &mm_lock_seq), vma);
}
static inline void vma_assert_locked(struct vm_area_struct *vma)
{
if (!rwsem_is_locked(&vma->vm_lock->lock))
vma_assert_write_locked(vma);
}
static inline void vma_mark_detached(struct vm_area_struct *vma, bool detached)
{
/* When detaching vma should be write-locked */
@ -737,6 +744,14 @@ 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);
@ -762,6 +777,11 @@ 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 */
extern const struct vm_operations_struct vma_dummy_vm_ops;

9
mm/memory.c
View file

@ -5471,14 +5471,7 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
* concurrent mremap() with MREMAP_DONTUNMAP could dissociate the VMA
* from its anon_vma.
*/
if (vma_is_anonymous(vma) && !vma->anon_vma)
goto inval_end_read;
/*
* 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))
if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma))
goto inval_end_read;
/* Check since vm_start/vm_end might change before we lock the VMA */