Re: [PATCH v6 3/3] userfaultfd: use per-vma locks in userfaultfd operations
From: Ryan Roberts
Date: Wed Feb 14 2024 - 17:12:46 EST
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:
[ 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@xxxxxxxxxx>
> ---
> 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);