Received-SPF: pass (google.com: domain of linux-kernel+bounces-66055-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
Message-ID: <dcf8ec3f-19cf-4b22-a2ce-5a6af5d1a51c@arm.com>
Date: Wed, 14 Feb 2024 22:33:04 +0000
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v6 3/3] userfaultfd: use per-vma locks in userfaultfd
 operations
Content-Language: en-GB
To: Lokesh Gidra <lokeshgidra@google.com>,
 Suren Baghdasaryan <surenb@google.com>
Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org,
 linux-mm@kvack.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org,
 kernel-team@android.com, aarcange@redhat.com, peterx@redhat.com,
 david@redhat.com, axelrasmussen@google.com, bgeffon@google.com,
 willy@infradead.org, jannh@google.com, kaleshsingh@google.com,
 ngeoffray@google.com, timmurray@google.com, rppt@kernel.org,
 Liam.Howlett@oracle.com
References: <20240213215741.3816570-1-lokeshgidra@google.com>
 <20240213215741.3816570-4-lokeshgidra@google.com>
 <855ee176-e628-489f-a3ee-cf0573cf5506@arm.com>
 <CAJuCfpFt7KOzzBV6hGO9TVHup3BaTRNQzjhz78MJEFPnn+Bhdg@mail.gmail.com>
 <CA+EESO6RKORqzK+nKr98QUDoK7p4ud5v9+5FfNM91eymVY+SJQ@mail.gmail.com>
From: Ryan Roberts <ryan.roberts@arm.com>
In-Reply-To: <CA+EESO6RKORqzK+nKr98QUDoK7p4ud5v9+5FfNM91eymVY+SJQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

On 14/02/2024 22:27, Lokesh Gidra wrote:
> On Wed, Feb 14, 2024 at 2:20 PM Suren Baghdasaryan <surenb@google.com> wrote:
>>
>> On Wed, Feb 14, 2024 at 2:12 PM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>>
>>> On 13/02/2024 21:57, Lokesh Gidra wrote:
>>>> All userfaultfd operations, except write-protect, opportunistically use
>>>> per-vma locks to lock vmas. On failure, attempt again inside mmap_lock
>>>> critical section.
>>>>
>>>> Write-protect operation requires mmap_lock as it iterates over multiple
>>>> vmas.
>>>
>>> Hi,
>>>
>>> I'm seeing the below OOPS when running on arm64 against mm-unstable. It can be reliably reproduced by running the `uffd-unit-tests` mm selftest. Bisecting mm-unstable leads to this patch:
>>>
>>> # bad: [649936c3db47f8f75b9b927e4edf5922a0f240a6] mm: add swappiness= arg to memory.reclaim
>>> git bisect bad 649936c3db47f8f75b9b927e4edf5922a0f240a6
>>> # good: [54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478] Linux 6.8-rc3
>>> git bisect good 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478
>>> # good: [10794cd18bb46c91c75fac44e551201cfe006baf] mm: zswap: warn when referencing a dead entry
>>> git bisect good 10794cd18bb46c91c75fac44e551201cfe006baf
>>> # good: [cb769b427edc7f46c7c764daa3421725bffdf315] mm-memcg-use-larger-batches-for-proactive-reclaim-v4
>>> git bisect good cb769b427edc7f46c7c764daa3421725bffdf315
>>> # good: [cfc5c1be4010c9972bc3f3d991235e8ea6928672] mm/z3fold: remove unneeded spinlock
>>> git bisect good cfc5c1be4010c9972bc3f3d991235e8ea6928672
>>> # good: [31094bce101651acb4747ab25d614bc893d65c89] kasan/test: avoid gcc warning for intentional overflow
>>> git bisect good 31094bce101651acb4747ab25d614bc893d65c89
>>> # bad: [55be0b2cd1fbf00e036e2e48ee0999599135af66] zram: do not allocate physically contiguous strm buffers
>>> git bisect bad 55be0b2cd1fbf00e036e2e48ee0999599135af66
>>> # good: [b11ca4a0a13024c0175dde56f9bd848803eddcd2] mm/mglru: improve swappiness handling
>>> git bisect good b11ca4a0a13024c0175dde56f9bd848803eddcd2
>>> # good: [22e7ccd57a1220afcd7c4da1f3005fd04d70014e] userfaultfd: move userfaultfd_ctx struct to header file
>>> git bisect good 22e7ccd57a1220afcd7c4da1f3005fd04d70014e
>>> # bad: [0a0d05338f13e64c9fb7ccd8f8d1793aaf33ec7d] userfaultfd: use per-vma locks in userfaultfd operations
>>> git bisect bad 0a0d05338f13e64c9fb7ccd8f8d1793aaf33ec7d
>>> # good: [8459e1c7acbe4442c6c0eef59825da1339e0a3cf] userfaultfd: protect mmap_changing with rw_sem in userfaulfd_ctx
>>> git bisect good 8459e1c7acbe4442c6c0eef59825da1339e0a3cf
>>> # first bad commit: [0a0d05338f13e64c9fb7ccd8f8d1793aaf33ec7d] userfaultfd: use per-vma locks in userfaultfd operations
>>>
>>> This is the oops:
>>
>> That's a call to mmap_assert_locked() from inside
>> move_pages_huge_pmd(). Since move_pages() are now happening under VMA
>> lock this call should be replaced with vma_assert_locked().
>>
> So sorry for missing this. I missed testing with CONFIG_DEBUG_VM
> turned on. I'll fix and thoroughly test before sending the next
> version.

No worries, I've reverted this patch in my branch and that's unblocked me, so
don't sweat it.

> 
>>>
>>> [   21.280142] mm ffff049340ed0000 task_size 281474976710656
>>> [   21.280142] get_unmapped_area ffffb3dbdc725e48
>>> [   21.280142] mmap_base 281474842492928 mmap_legacy_base 0
>>> [   21.280142] pgd ffff04935829a000 mm_users 3 mm_count 4 pgtables_bytes 98304 map_count 21
>>> [   21.280142] hiwater_rss 2167 hiwater_vm 8234 total_vm 4a44 locked_vm 0
>>> [   21.280142] pinned_vm 0 data_vm 4835 exec_vm 1c6 stack_vm 21
>>> [   21.280142] start_code aaaaaaaa0000 end_code aaaaaaab1b28 start_data aaaaaaac2a60 end_data aaaaaaac3410
>>> [   21.280142] start_brk aaaaaaac5000 brk aaaaaaae6000 start_stack fffffffff6b0
>>> [   21.280142] arg_start fffffffff8c7 arg_end fffffffff8e2 env_start fffffffff8e2 env_end ffffffffffdd
>>> [   21.280142] binfmt ffffb3dbdf2f8cf8 flags 82008d
>>> [   21.280142] ioctx_table 0000000000000000
>>> [   21.280142] owner ffff049311f02280 exe_file ffff049355314c00
>>> [   21.280142] notifier_subscriptions 0000000000000000
>>> [   21.280142] numa_next_scan 4294897864 numa_scan_offset 0 numa_scan_seq 0
>>> [   21.280142] tlb_flush_pending 0
>>> [   21.280142] def_flags: 0x0()
>>> [   21.283302] kernel BUG at include/linux/mmap_lock.h:66!
>>> [   21.283481] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
>>> [   21.283720] Modules linked in:
>>> [   21.283867] CPU: 3 PID: 1226 Comm: uffd-unit-tests Not tainted 6.8.0-rc3-00297-g0a0d05338f13 #19
>>> [   21.284306] Hardware name: linux,dummy-virt (DT)
>>> [   21.284495] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
>>> [   21.284833] pc : move_pages_huge_pmd+0x4d0/0x8a8
>>> [   21.285072] lr : move_pages_huge_pmd+0x4d0/0x8a8
>>> [   21.285289] sp : ffff800088573b30
>>> [   21.285439] x29: ffff800088573b30 x28: ffff049358292d78 x27: fffffc0000000000
>>> [   21.285770] x26: ffff049358292d78 x25: 0000fffff5e00000 x24: ffff049359db3730
>>> [   21.286097] x23: 0000fffff6000000 x22: ffff049340ed0000 x21: ffff049359db3678
>>> [   21.286422] x20: 0000000000000002 x19: fffffc124d60a480 x18: 0000000000000006
>>> [   21.286747] x17: 626c740a30207165 x16: 735f6e6163735f61 x15: 6d756e2030207465
>>> [   21.287084] x14: 7366666f5f6e6163 x13: 2928307830203a73 x12: 67616c665f666564
>>> [   21.287417] x11: 0a3020676e69646e x10: ffffb3dbdf28bff8 x9 : ffffb3dbdc620f80
>>> [   21.287745] x8 : 00000000ffffefff x7 : ffffb3dbdf28bff8 x6 : 80000000fffff000
>>> [   21.288082] x5 : ffff04933ffdcd08 x4 : 0000000000000000 x3 : 0000000000000000
>>> [   21.288364] x2 : 0000000000000000 x1 : ffff049340106780 x0 : 0000000000000328
>>> [   21.288712] Call trace:
>>> [   21.288832]  move_pages_huge_pmd+0x4d0/0x8a8
>>> [   21.289058]  move_pages+0x8b8/0x13d8
>>> [   21.289205]  userfaultfd_ioctl+0x11e0/0x1e90
>>> [   21.289411]  __arm64_sys_ioctl+0xb4/0x100
>>> [   21.289579]  invoke_syscall+0x50/0x128
>>> [   21.289738]  el0_svc_common.constprop.0+0x48/0xf0
>>> [   21.289942]  do_el0_svc+0x24/0x38
>>> [   21.290078]  el0_svc+0x34/0xb8
>>> [   21.290219]  el0t_64_sync_handler+0x100/0x130
>>> [   21.290387]  el0t_64_sync+0x190/0x198
>>> [   21.290535] Code: 17ffff7e a90363f7 a9046bf9 97fde2a7 (d4210000)
>>> [   21.290776] ---[ end trace 0000000000000000 ]---
>>> [   21.290966] note: uffd-unit-tests[1226] exited with irqs disabled
>>> [   21.291254] note: uffd-unit-tests[1226] exited with preempt_count 2
>>> [   21.292864] ------------[ cut here ]------------
>>> [   21.293020] WARNING: CPU: 3 PID: 0 at kernel/context_tracking.c:128 ct_kernel_exit.constprop.0+0x108/0x120
>>> [   21.293711] Modules linked in:
>>> [   21.294070] CPU: 3 PID: 0 Comm: swapper/3 Tainted: G      D            6.8.0-rc3-00297-g0a0d05338f13 #19
>>> [   21.295447] Hardware name: linux,dummy-virt (DT)
>>> [   21.295850] pstate: 214003c5 (nzCv DAIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
>>> [   21.296152] pc : ct_kernel_exit.constprop.0+0x108/0x120
>>> [   21.296685] lr : ct_idle_enter+0x10/0x20
>>> [   21.296848] sp : ffff8000801b3dc0
>>> [   21.296983] x29: ffff8000801b3dc0 x28: 0000000000000000 x27: 0000000000000000
>>> [   21.297255] x26: 0000000000000000 x25: ffff049301496780 x24: 0000000000000000
>>> [   21.297533] x23: 0000000000000000 x22: ffff049301496780 x21: ffffb3dbdf209ae0
>>> [   21.297844] x20: ffffb3dbdf209a20 x19: ffff04933ffeace0 x18: ffff800088573648
>>> [   21.298152] x17: ffffb3dbdf65def0 x16: 00000000d72145a7 x15: 00000000f1a17b35
>>> [   21.298439] x14: 0000000000000004 x13: ffffb3dbdf22c3a8 x12: 0000000000000000
>>> [   21.298738] x11: ffff0493541472a8 x10: 2b58349b7608bfc4 x9 : ffffb3dbdc57f43c
>>> [   21.299031] x8 : ffff049301497858 x7 : 00000000000001c1 x6 : 000000001eeeb49c
>>> [   21.299329] x5 : 4000000000000002 x4 : ffff50b7618d7000 x3 : ffff8000801b3dc0
>>> [   21.299615] x2 : ffffb3dbde713ce0 x1 : 4000000000000000 x0 : ffffb3dbde713ce0
>>> [   21.299900] Call trace:
>>> [   21.299998]  ct_kernel_exit.constprop.0+0x108/0x120
>>> [   21.300460]  ct_idle_enter+0x10/0x20
>>> [   21.300690]  default_idle_call+0x3c/0x170
>>> [   21.300861]  do_idle+0x218/0x278
>>> [   21.300992]  cpu_startup_entry+0x3c/0x50
>>> [   21.301148]  secondary_start_kernel+0x130/0x158
>>> [   21.301329]  __secondary_switched+0xb8/0xc0
>>> [   21.301641] ---[ end trace 0000000000000000 ]---
>>>
>>>
>>> Can this series be removed from mm-unstable until fixed, please?
>>>
>>> Thanks,
>>> Ryan
>>>
>>>
>>>>
>>>> Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
>>>> ---
>>>>  fs/userfaultfd.c              |  13 +-
>>>>  include/linux/userfaultfd_k.h |   5 +-
>>>>  mm/userfaultfd.c              | 380 ++++++++++++++++++++++++++--------
>>>>  3 files changed, 296 insertions(+), 102 deletions(-)
>>>>
>>>> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
>>>> index c00a021bcce4..60dcfafdc11a 100644
>>>> --- a/fs/userfaultfd.c
>>>> +++ b/fs/userfaultfd.c
>>>> @@ -2005,17 +2005,8 @@ static int userfaultfd_move(struct userfaultfd_ctx *ctx,
>>>>               return -EINVAL;
>>>>
>>>>       if (mmget_not_zero(mm)) {
>>>> -             mmap_read_lock(mm);
>>>> -
>>>> -             /* Re-check after taking map_changing_lock */
>>>> -             down_read(&ctx->map_changing_lock);
>>>> -             if (likely(!atomic_read(&ctx->mmap_changing)))
>>>> -                     ret = move_pages(ctx, mm, uffdio_move.dst, uffdio_move.src,
>>>> -                                      uffdio_move.len, uffdio_move.mode);
>>>> -             else
>>>> -                     ret = -EAGAIN;
>>>> -             up_read(&ctx->map_changing_lock);
>>>> -             mmap_read_unlock(mm);
>>>> +             ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src,
>>>> +                              uffdio_move.len, uffdio_move.mode);
>>>>               mmput(mm);
>>>>       } else {
>>>>               return -ESRCH;
>>>> diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
>>>> index 3210c3552976..05d59f74fc88 100644
>>>> --- a/include/linux/userfaultfd_k.h
>>>> +++ b/include/linux/userfaultfd_k.h
>>>> @@ -138,9 +138,8 @@ extern long uffd_wp_range(struct vm_area_struct *vma,
>>>>  /* move_pages */
>>>>  void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2);
>>>>  void double_pt_unlock(spinlock_t *ptl1, spinlock_t *ptl2);
>>>> -ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
>>>> -                unsigned long dst_start, unsigned long src_start,
>>>> -                unsigned long len, __u64 flags);
>>>> +ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
>>>> +                unsigned long src_start, unsigned long len, __u64 flags);
>>>>  int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pmd_t dst_pmdval,
>>>>                       struct vm_area_struct *dst_vma,
>>>>                       struct vm_area_struct *src_vma,
>>>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
>>>> index 74aad0831e40..4744d6a96f96 100644
>>>> --- a/mm/userfaultfd.c
>>>> +++ b/mm/userfaultfd.c
>>>> @@ -20,19 +20,11 @@
>>>>  #include "internal.h"
>>>>
>>>>  static __always_inline
>>>> -struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
>>>> -                                 unsigned long dst_start,
>>>> -                                 unsigned long len)
>>>> +bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end)
>>>>  {
>>>> -     /*
>>>> -      * Make sure that the dst range is both valid and fully within a
>>>> -      * single existing vma.
>>>> -      */
>>>> -     struct vm_area_struct *dst_vma;
>>>> -
>>>> -     dst_vma = find_vma(dst_mm, dst_start);
>>>> -     if (!range_in_vma(dst_vma, dst_start, dst_start + len))
>>>> -             return NULL;
>>>> +     /* Make sure that the dst range is fully within dst_vma. */
>>>> +     if (dst_end > dst_vma->vm_end)
>>>> +             return false;
>>>>
>>>>       /*
>>>>        * Check the vma is registered in uffd, this is required to
>>>> @@ -40,11 +32,122 @@ struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
>>>>        * time.
>>>>        */
>>>>       if (!dst_vma->vm_userfaultfd_ctx.ctx)
>>>> -             return NULL;
>>>> +             return false;
>>>> +
>>>> +     return true;
>>>> +}
>>>> +
>>>> +static __always_inline
>>>> +struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
>>>> +                                              unsigned long addr)
>>>> +{
>>>> +     struct vm_area_struct *vma;
>>>> +
>>>> +     mmap_assert_locked(mm);
>>>> +     vma = vma_lookup(mm, addr);
>>>> +     if (!vma)
>>>> +             vma = ERR_PTR(-ENOENT);
>>>> +     else if (!(vma->vm_flags & VM_SHARED) &&
>>>> +              unlikely(anon_vma_prepare(vma)))
>>>> +             vma = ERR_PTR(-ENOMEM);
>>>> +
>>>> +     return vma;
>>>> +}
>>>> +
>>>> +#ifdef CONFIG_PER_VMA_LOCK
>>>> +/*
>>>> + * lock_vma() - Lookup and lock vma corresponding to @address.
>>>> + * @mm: mm to search vma in.
>>>> + * @address: address that the vma should contain.
>>>> + *
>>>> + * Should be called without holding mmap_lock. vma should be unlocked after use
>>>> + * with unlock_vma().
>>>> + *
>>>> + * Return: A locked vma containing @address, -ENOENT if no vma is found, or
>>>> + * -ENOMEM if anon_vma couldn't be allocated.
>>>> + */
>>>> +static struct vm_area_struct *lock_vma(struct mm_struct *mm,
>>>> +                                    unsigned long address)
>>>> +{
>>>> +     struct vm_area_struct *vma;
>>>> +
>>>> +     vma = lock_vma_under_rcu(mm, address);
>>>> +     if (vma) {
>>>> +             /*
>>>> +              * lock_vma_under_rcu() only checks anon_vma for private
>>>> +              * anonymous mappings. But we need to ensure it is assigned in
>>>> +              * private file-backed vmas as well.
>>>> +              */
>>>> +             if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma))
>>>> +                     vma_end_read(vma);
>>>> +             else
>>>> +                     return vma;
>>>> +     }
>>>> +
>>>> +     mmap_read_lock(mm);
>>>> +     vma = find_vma_and_prepare_anon(mm, address);
>>>> +     if (!IS_ERR(vma)) {
>>>> +             /*
>>>> +              * We cannot use vma_start_read() as it may fail due to
>>>> +              * false locked (see comment in vma_start_read()). We
>>>> +              * can avoid that by directly locking vm_lock under
>>>> +              * mmap_lock, which guarantees that nobody can lock the
>>>> +              * vma for write (vma_start_write()) under us.
>>>> +              */
>>>> +             down_read(&vma->vm_lock->lock);
>>>> +     }
>>>> +
>>>> +     mmap_read_unlock(mm);
>>>> +     return vma;
>>>> +}
>>>> +
>>>> +static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
>>>> +                                           unsigned long dst_start,
>>>> +                                           unsigned long len)
>>>> +{
>>>> +     struct vm_area_struct *dst_vma;
>>>>
>>>> +     dst_vma = lock_vma(dst_mm, dst_start);
>>>> +     if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len))
>>>> +             return dst_vma;
>>>> +
>>>> +     vma_end_read(dst_vma);
>>>> +     return ERR_PTR(-ENOENT);
>>>> +}
>>>> +
>>>> +static void uffd_mfill_unlock(struct vm_area_struct *vma)
>>>> +{
>>>> +     vma_end_read(vma);
>>>> +}
>>>> +
>>>> +#else
>>>> +
>>>> +static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
>>>> +                                           unsigned long dst_start,
>>>> +                                           unsigned long len)
>>>> +{
>>>> +     struct vm_area_struct *dst_vma;
>>>> +
>>>> +     mmap_read_lock(dst_mm);
>>>> +     dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start);
>>>> +     if (IS_ERR(dst_vma))
>>>> +             goto out_unlock;
>>>> +
>>>> +     if (validate_dst_vma(dst_vma, dst_start + len))
>>>> +             return dst_vma;
>>>> +
>>>> +     dst_vma = ERR_PTR(-ENOENT);
>>>> +out_unlock:
>>>> +     mmap_read_unlock(dst_mm);
>>>>       return dst_vma;
>>>>  }
>>>>
>>>> +static void uffd_mfill_unlock(struct vm_area_struct *vma)
>>>> +{
>>>> +     mmap_read_unlock(vma->vm_mm);
>>>> +}
>>>> +#endif
>>>> +
>>>>  /* Check if dst_addr is outside of file's size. Must be called with ptl held. */
>>>>  static bool mfill_file_over_size(struct vm_area_struct *dst_vma,
>>>>                                unsigned long dst_addr)
>>>> @@ -350,7 +453,8 @@ static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
>>>>  #ifdef CONFIG_HUGETLB_PAGE
>>>>  /*
>>>>   * mfill_atomic processing for HUGETLB vmas.  Note that this routine is
>>>> - * called with mmap_lock held, it will release mmap_lock before returning.
>>>> + * called with either vma-lock or mmap_lock held, it will release the lock
>>>> + * before returning.
>>>>   */
>>>>  static __always_inline ssize_t mfill_atomic_hugetlb(
>>>>                                             struct userfaultfd_ctx *ctx,
>>>> @@ -361,7 +465,6 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
>>>>                                             uffd_flags_t flags)
>>>>  {
>>>>       struct mm_struct *dst_mm = dst_vma->vm_mm;
>>>> -     int vm_shared = dst_vma->vm_flags & VM_SHARED;
>>>>       ssize_t err;
>>>>       pte_t *dst_pte;
>>>>       unsigned long src_addr, dst_addr;
>>>> @@ -380,7 +483,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
>>>>        */
>>>>       if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
>>>>               up_read(&ctx->map_changing_lock);
>>>> -             mmap_read_unlock(dst_mm);
>>>> +             uffd_mfill_unlock(dst_vma);
>>>>               return -EINVAL;
>>>>       }
>>>>
>>>> @@ -403,24 +506,28 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
>>>>        * retry, dst_vma will be set to NULL and we must lookup again.
>>>>        */
>>>>       if (!dst_vma) {
>>>> +             dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
>>>> +             if (IS_ERR(dst_vma)) {
>>>> +                     err = PTR_ERR(dst_vma);
>>>> +                     goto out;
>>>> +             }
>>>> +
>>>>               err = -ENOENT;
>>>> -             dst_vma = find_dst_vma(dst_mm, dst_start, len);
>>>> -             if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
>>>> -                     goto out_unlock;
>>>> +             if (!is_vm_hugetlb_page(dst_vma))
>>>> +                     goto out_unlock_vma;
>>>>
>>>>               err = -EINVAL;
>>>>               if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
>>>> -                     goto out_unlock;
>>>> -
>>>> -             vm_shared = dst_vma->vm_flags & VM_SHARED;
>>>> -     }
>>>> +                     goto out_unlock_vma;
>>>>
>>>> -     /*
>>>> -      * If not shared, ensure the dst_vma has a anon_vma.
>>>> -      */
>>>> -     err = -ENOMEM;
>>>> -     if (!vm_shared) {
>>>> -             if (unlikely(anon_vma_prepare(dst_vma)))
>>>> +             /*
>>>> +              * If memory mappings are changing because of non-cooperative
>>>> +              * operation (e.g. mremap) running in parallel, bail out and
>>>> +              * request the user to retry later
>>>> +              */
>>>> +             down_read(&ctx->map_changing_lock);
>>>> +             err = -EAGAIN;
>>>> +             if (atomic_read(&ctx->mmap_changing))
>>>>                       goto out_unlock;
>>>>       }
>>>>
>>>> @@ -465,7 +572,7 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
>>>>
>>>>               if (unlikely(err == -ENOENT)) {
>>>>                       up_read(&ctx->map_changing_lock);
>>>> -                     mmap_read_unlock(dst_mm);
>>>> +                     uffd_mfill_unlock(dst_vma);
>>>>                       BUG_ON(!folio);
>>>>
>>>>                       err = copy_folio_from_user(folio,
>>>> @@ -474,17 +581,6 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
>>>>                               err = -EFAULT;
>>>>                               goto out;
>>>>                       }
>>>> -                     mmap_read_lock(dst_mm);
>>>> -                     down_read(&ctx->map_changing_lock);
>>>> -                     /*
>>>> -                      * If memory mappings are changing because of non-cooperative
>>>> -                      * operation (e.g. mremap) running in parallel, bail out and
>>>> -                      * request the user to retry later
>>>> -                      */
>>>> -                     if (atomic_read(&ctx->mmap_changing)) {
>>>> -                             err = -EAGAIN;
>>>> -                             break;
>>>> -                     }
>>>>
>>>>                       dst_vma = NULL;
>>>>                       goto retry;
>>>> @@ -505,7 +601,8 @@ static __always_inline ssize_t mfill_atomic_hugetlb(
>>>>
>>>>  out_unlock:
>>>>       up_read(&ctx->map_changing_lock);
>>>> -     mmap_read_unlock(dst_mm);
>>>> +out_unlock_vma:
>>>> +     uffd_mfill_unlock(dst_vma);
>>>>  out:
>>>>       if (folio)
>>>>               folio_put(folio);
>>>> @@ -597,7 +694,15 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
>>>>       copied = 0;
>>>>       folio = NULL;
>>>>  retry:
>>>> -     mmap_read_lock(dst_mm);
>>>> +     /*
>>>> +      * Make sure the vma is not shared, that the dst range is
>>>> +      * both valid and fully within a single existing vma.
>>>> +      */
>>>> +     dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
>>>> +     if (IS_ERR(dst_vma)) {
>>>> +             err = PTR_ERR(dst_vma);
>>>> +             goto out;
>>>> +     }
>>>>
>>>>       /*
>>>>        * If memory mappings are changing because of non-cooperative
>>>> @@ -609,15 +714,6 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
>>>>       if (atomic_read(&ctx->mmap_changing))
>>>>               goto out_unlock;
>>>>
>>>> -     /*
>>>> -      * Make sure the vma is not shared, that the dst range is
>>>> -      * both valid and fully within a single existing vma.
>>>> -      */
>>>> -     err = -ENOENT;
>>>> -     dst_vma = find_dst_vma(dst_mm, dst_start, len);
>>>> -     if (!dst_vma)
>>>> -             goto out_unlock;
>>>> -
>>>>       err = -EINVAL;
>>>>       /*
>>>>        * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
>>>> @@ -647,16 +743,6 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
>>>>           uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))
>>>>               goto out_unlock;
>>>>
>>>> -     /*
>>>> -      * Ensure the dst_vma has a anon_vma or this page
>>>> -      * would get a NULL anon_vma when moved in the
>>>> -      * dst_vma.
>>>> -      */
>>>> -     err = -ENOMEM;
>>>> -     if (!(dst_vma->vm_flags & VM_SHARED) &&
>>>> -         unlikely(anon_vma_prepare(dst_vma)))
>>>> -             goto out_unlock;
>>>> -
>>>>       while (src_addr < src_start + len) {
>>>>               pmd_t dst_pmdval;
>>>>
>>>> @@ -699,7 +785,7 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
>>>>                       void *kaddr;
>>>>
>>>>                       up_read(&ctx->map_changing_lock);
>>>> -                     mmap_read_unlock(dst_mm);
>>>> +                     uffd_mfill_unlock(dst_vma);
>>>>                       BUG_ON(!folio);
>>>>
>>>>                       kaddr = kmap_local_folio(folio, 0);
>>>> @@ -730,7 +816,7 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
>>>>
>>>>  out_unlock:
>>>>       up_read(&ctx->map_changing_lock);
>>>> -     mmap_read_unlock(dst_mm);
>>>> +     uffd_mfill_unlock(dst_vma);
>>>>  out:
>>>>       if (folio)
>>>>               folio_put(folio);
>>>> @@ -1267,27 +1353,136 @@ static int validate_move_areas(struct userfaultfd_ctx *ctx,
>>>>       if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma))
>>>>               return -EINVAL;
>>>>
>>>> +     return 0;
>>>> +}
>>>> +
>>>> +static __always_inline
>>>> +int find_vmas_mm_locked(struct mm_struct *mm,
>>>> +                     unsigned long dst_start,
>>>> +                     unsigned long src_start,
>>>> +                     struct vm_area_struct **dst_vmap,
>>>> +                     struct vm_area_struct **src_vmap)
>>>> +{
>>>> +     struct vm_area_struct *vma;
>>>> +
>>>> +     mmap_assert_locked(mm);
>>>> +     vma = find_vma_and_prepare_anon(mm, dst_start);
>>>> +     if (IS_ERR(vma))
>>>> +             return PTR_ERR(vma);
>>>> +
>>>> +     *dst_vmap = vma;
>>>> +     /* Skip finding src_vma if src_start is in dst_vma */
>>>> +     if (src_start >= vma->vm_start && src_start < vma->vm_end)
>>>> +             goto out_success;
>>>> +
>>>> +     vma = vma_lookup(mm, src_start);
>>>> +     if (!vma)
>>>> +             return -ENOENT;
>>>> +out_success:
>>>> +     *src_vmap = vma;
>>>> +     return 0;
>>>> +}
>>>> +
>>>> +#ifdef CONFIG_PER_VMA_LOCK
>>>> +static int uffd_move_lock(struct mm_struct *mm,
>>>> +                       unsigned long dst_start,
>>>> +                       unsigned long src_start,
>>>> +                       struct vm_area_struct **dst_vmap,
>>>> +                       struct vm_area_struct **src_vmap)
>>>> +{
>>>> +     struct vm_area_struct *vma;
>>>> +     int err;
>>>> +
>>>> +     vma = lock_vma(mm, dst_start);
>>>> +     if (IS_ERR(vma))
>>>> +             return PTR_ERR(vma);
>>>> +
>>>> +     *dst_vmap = vma;
>>>>       /*
>>>> -      * Ensure the dst_vma has a anon_vma or this page
>>>> -      * would get a NULL anon_vma when moved in the
>>>> -      * dst_vma.
>>>> +      * Skip finding src_vma if src_start is in dst_vma. This also ensures
>>>> +      * that we don't lock the same vma twice.
>>>>        */
>>>> -     if (unlikely(anon_vma_prepare(dst_vma)))
>>>> -             return -ENOMEM;
>>>> +     if (src_start >= vma->vm_start && src_start < vma->vm_end) {
>>>> +             *src_vmap = vma;
>>>> +             return 0;
>>>> +     }
>>>>
>>>> -     return 0;
>>>> +     /*
>>>> +      * Using lock_vma() to get src_vma can lead to following deadlock:
>>>> +      *
>>>> +      * Thread1                              Thread2
>>>> +      * -------                              -------
>>>> +      * vma_start_read(dst_vma)
>>>> +      *                                      mmap_write_lock(mm)
>>>> +      *                                      vma_start_write(src_vma)
>>>> +      * vma_start_read(src_vma)
>>>> +      * mmap_read_lock(mm)
>>>> +      *                                      vma_start_write(dst_vma)
>>>> +      */
>>>> +     *src_vmap = lock_vma_under_rcu(mm, src_start);
>>>> +     if (likely(*src_vmap))
>>>> +             return 0;
>>>> +
>>>> +     /* Undo any locking and retry in mmap_lock critical section */
>>>> +     vma_end_read(*dst_vmap);
>>>> +
>>>> +     mmap_read_lock(mm);
>>>> +     err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
>>>> +     if (!err) {
>>>> +             /*
>>>> +              * See comment in lock_vma() as to why not using
>>>> +              * vma_start_read() here.
>>>> +              */
>>>> +             down_read(&(*dst_vmap)->vm_lock->lock);
>>>> +             if (*dst_vmap != *src_vmap)
>>>> +                     down_read(&(*src_vmap)->vm_lock->lock);
>>>> +     }
>>>> +     mmap_read_unlock(mm);
>>>> +     return err;
>>>> +}
>>>> +
>>>> +static void uffd_move_unlock(struct vm_area_struct *dst_vma,
>>>> +                          struct vm_area_struct *src_vma)
>>>> +{
>>>> +     vma_end_read(src_vma);
>>>> +     if (src_vma != dst_vma)
>>>> +             vma_end_read(dst_vma);
>>>>  }
>>>>
>>>> +#else
>>>> +
>>>> +static int uffd_move_lock(struct mm_struct *mm,
>>>> +                       unsigned long dst_start,
>>>> +                       unsigned long src_start,
>>>> +                       struct vm_area_struct **dst_vmap,
>>>> +                       struct vm_area_struct **src_vmap)
>>>> +{
>>>> +     int err;
>>>> +
>>>> +     mmap_read_lock(mm);
>>>> +     err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
>>>> +     if (err)
>>>> +             mmap_read_unlock(mm);
>>>> +     return err;
>>>> +}
>>>> +
>>>> +static void uffd_move_unlock(struct vm_area_struct *dst_vma,
>>>> +                          struct vm_area_struct *src_vma)
>>>> +{
>>>> +     mmap_assert_locked(src_vma->vm_mm);
>>>> +     mmap_read_unlock(dst_vma->vm_mm);
>>>> +}
>>>> +#endif
>>>> +
>>>>  /**
>>>>   * move_pages - move arbitrary anonymous pages of an existing vma
>>>>   * @ctx: pointer to the userfaultfd context
>>>> - * @mm: the address space to move pages
>>>>   * @dst_start: start of the destination virtual memory range
>>>>   * @src_start: start of the source virtual memory range
>>>>   * @len: length of the virtual memory range
>>>>   * @mode: flags from uffdio_move.mode
>>>>   *
>>>> - * Must be called with mmap_lock held for read.
>>>> + * It will either use the mmap_lock in read mode or per-vma locks
>>>>   *
>>>>   * move_pages() remaps arbitrary anonymous pages atomically in zero
>>>>   * copy. It only works on non shared anonymous pages because those can
>>>> @@ -1355,10 +1550,10 @@ static int validate_move_areas(struct userfaultfd_ctx *ctx,
>>>>   * could be obtained. This is the only additional complexity added to
>>>>   * the rmap code to provide this anonymous page remapping functionality.
>>>>   */
>>>> -ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
>>>> -                unsigned long dst_start, unsigned long src_start,
>>>> -                unsigned long len, __u64 mode)
>>>> +ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
>>>> +                unsigned long src_start, unsigned long len, __u64 mode)
>>>>  {
>>>> +     struct mm_struct *mm = ctx->mm;
>>>>       struct vm_area_struct *src_vma, *dst_vma;
>>>>       unsigned long src_addr, dst_addr;
>>>>       pmd_t *src_pmd, *dst_pmd;
>>>> @@ -1376,28 +1571,34 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
>>>>           WARN_ON_ONCE(dst_start + len <= dst_start))
>>>>               goto out;
>>>>
>>>> +     err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma);
>>>> +     if (err)
>>>> +             goto out;
>>>> +
>>>> +     /* Re-check after taking map_changing_lock */
>>>> +     err = -EAGAIN;
>>>> +     down_read(&ctx->map_changing_lock);
>>>> +     if (likely(atomic_read(&ctx->mmap_changing)))
>>>> +             goto out_unlock;
>>>>       /*
>>>>        * Make sure the vma is not shared, that the src and dst remap
>>>>        * ranges are both valid and fully within a single existing
>>>>        * vma.
>>>>        */
>>>> -     src_vma = find_vma(mm, src_start);
>>>> -     if (!src_vma || (src_vma->vm_flags & VM_SHARED))
>>>> -             goto out;
>>>> -     if (src_start < src_vma->vm_start ||
>>>> -         src_start + len > src_vma->vm_end)
>>>> -             goto out;
>>>> +     err = -EINVAL;
>>>> +     if (src_vma->vm_flags & VM_SHARED)
>>>> +             goto out_unlock;
>>>> +     if (src_start + len > src_vma->vm_end)
>>>> +             goto out_unlock;
>>>>
>>>> -     dst_vma = find_vma(mm, dst_start);
>>>> -     if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
>>>> -             goto out;
>>>> -     if (dst_start < dst_vma->vm_start ||
>>>> -         dst_start + len > dst_vma->vm_end)
>>>> -             goto out;
>>>> +     if (dst_vma->vm_flags & VM_SHARED)
>>>> +             goto out_unlock;
>>>> +     if (dst_start + len > dst_vma->vm_end)
>>>> +             goto out_unlock;
>>>>
>>>>       err = validate_move_areas(ctx, src_vma, dst_vma);
>>>>       if (err)
>>>> -             goto out;
>>>> +             goto out_unlock;
>>>>
>>>>       for (src_addr = src_start, dst_addr = dst_start;
>>>>            src_addr < src_start + len;) {
>>>> @@ -1514,6 +1715,9 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
>>>>               moved += step_size;
>>>>       }
>>>>
>>>> +out_unlock:
>>>> +     up_read(&ctx->map_changing_lock);
>>>> +     uffd_move_unlock(dst_vma, src_vma);
>>>>  out:
>>>>       VM_WARN_ON(moved < 0);
>>>>       VM_WARN_ON(err > 0);
>>>
>>> --
>>> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.
>>>