Re: [PATCH] mm/memory: Fix spurious warning when unmapping device-private/exclusive pages

[Lorenzo Stoakes <ljs@kernel.org>]

On Fri, May 01, 2026 at 04:51:16PM +1000, Alistair Popple wrote:
> Device private and exclusive entries are only supported for anonymous
> folios. This condition is tested in __migrate_device_pages() and
> make_device_exclusive() using folio_test_anon(). However the unmap path
> tests this assumption using vma_is_anonymous().
>
> This is wrong because whilst anonymous VMAs can only contain folios
> where folio_test_anon() is true the opposite relation does not
> hold. A folio for which folio_test_anon() is true does not imply
> vma_is_anonymous() is true. Such a condition can occur if for example a
> folio is part of a private filebacked mapping.

Yes this is a classic case of anon _VMA_ vs. anon _folio_ :) and it's our good
friend MAP_PRIVATE file-backed mappings at play also.

>
> In this case vma_is_anonymous() is false as the mapping is filebacked,
> but folio_test_anon() may be true, thus permitting devices to migrate
> the folio to device private memory. This can lead to the following
> spurious warnings during process teardown:
>
> [  772.737706] ------------[ cut here ]------------
> [  772.739201] WARNING: mm/memory.c:1754 at unmap_page_range.cold+0x26/0x18a, CPU#17: hmm-tests/2041
> [  772.742050] Modules linked in: test_hmm nvidia_uvm(O) nvidia(O)
> [  772.743959] CPU: 17 UID: 0 PID: 2041 Comm: hmm-tests Tainted: G        W  O        7.0.0+ #387 PREEMPT(full)
> [  772.747104] Tainted: [W]=WARN, [O]=OOT_MODULE
> [  772.748509] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
> [  772.752117] RIP: 0010:unmap_page_range.cold+0x26/0x18a
> [  772.753780] Code: 7e fe ff ff 48 89 4c 24 78 4c 89 44 24 38 e8 f2 ff b1 00 48 8b 4c 24 78 4c 8b 44 24 38 48 8b 44 24 18 48 83 78 48 00 74 04 90 <0f> 0b 90 48 89 ca b8 ff ff 37 00 48 c1 ea 03 48 c1 e0 2a 80 3c 02
> [  772.759602] RSP: 0018:ffff888112607550 EFLAGS: 00010286
> [  772.761310] RAX: ffff88811bbf4dc0 RBX: dffffc0000000000 RCX: ffffea03e9bfffd8
> [  772.763583] RDX: 1ffff1102377e9c1 RSI: 0000000000000008 RDI: ffff88811bbf4e08
> [  772.765914] RBP: 0000000000000006 R08: ffff8881059f7448 R09: ffffed10224c0e68
> [  772.768184] R10: ffff888112607347 R11: 0000000000000001 R12: 0000000000000001
> [  772.770461] R13: ffffea03e9bfffc0 R14: ffff888112607908 R15: ffffea03e9bfffc0
> [  772.772782] FS:  00007f327caa2780(0000) GS:ffff888427b7d000(0000) knlGS:0000000000000000
> [  772.775328] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  772.777187] CR2: 00007f327ca89000 CR3: 00000001994d5000 CR4: 00000000000006f0
> [  772.779135] Call Trace:
> [  772.779792]  <TASK>
> [  772.780317]  ? dmirror_interval_invalidate+0x1a3/0x290 [test_hmm]
> [  772.781873]  ? vm_normal_page_pud+0x2b0/0x2b0
> [  772.782992]  ? __rwlock_init+0x150/0x150
> [  772.784006]  ? lock_release+0x216/0x2b0
> [  772.785008]  ? __mmu_notifier_invalidate_range_start+0x505/0x6e0
> [  772.786522]  ? lock_release+0x216/0x2b0
> [  772.787498]  ? unmap_single_vma+0xb6/0x210
> [  772.788573]  unmap_vmas+0x27d/0x520
> [  772.789506]  ? unmap_single_vma+0x210/0x210
> [  772.790607]  ? mas_update_gap.part.0+0x620/0x620
> [  772.791834]  unmap_region+0x19e/0x350
> [  772.792769]  ? remove_vma+0x130/0x130
> [  772.793684]  ? mas_alloc_nodes+0x1f2/0x300
> [  772.794730]  vms_complete_munmap_vmas+0x8c1/0xe20
> [  772.795926]  ? unmap_region+0x350/0x350
> [  772.796917]  do_vmi_align_munmap+0x36a/0x4e0
> [  772.798018]  ? lock_release+0x216/0x2b0
> [  772.799024]  ? vma_shrink+0x620/0x620
> [  772.799983]  do_vmi_munmap+0x150/0x2c0
> [  772.800939]  __vm_munmap+0x161/0x2c0
> [  772.801872]  ? expand_downwards+0xd60/0xd60
> [  772.802948]  ? clockevents_program_event+0x1ef/0x540
> [  772.804217]  ? lock_release+0x216/0x2b0
> [  772.805158]  __x64_sys_munmap+0x59/0x80
> [  772.805776]  do_syscall_64+0xfc/0x670
> [  772.806336]  ? irqentry_exit+0xda/0x580
> [  772.806976]  entry_SYSCALL_64_after_hwframe+0x4b/0x53
> [  772.807772] RIP: 0033:0x7f327cbb2717
> [  772.808323] Code: 73 01 c3 48 8b 0d f9 76 0d 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 0b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d c9 76 0d 00 f7 d8 64 89 01 48
> [  772.811337] RSP: 002b:00007ffde7f57d38 EFLAGS: 00000202 ORIG_RAX: 000000000000000b
> [  772.812564] RAX: ffffffffffffffda RBX: 00007f327cc9c000 RCX: 00007f327cbb2717
> [  772.813733] RDX: 0000000000000000 RSI: 0000000000400000 RDI: 00007f327c289000
> [  772.814867] RBP: 0000000000421360 R08: 000000000000001a R09: 0000000000000000
> [  772.815991] R10: 0000000000000003 R11: 0000000000000202 R12: 00007ffde7f57d74
> [  772.817121] R13: 00007f327c689010 R14: 0000000000100000 R15: 00007f327c289000
> [  772.818272]  </TASK>
> [  772.818614] irq event stamp: 0
> [  772.819159] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
> [  772.820174] hardirqs last disabled at (0): [<ffffffff82a57ab3>] copy_process+0x19f3/0x6440
> [  772.821511] softirqs last  enabled at (0): [<ffffffff82a57b00>] copy_process+0x1a40/0x6440
> [  772.822869] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [  772.823871] ---[ end trace 0000000000000000 ]---
>
> Fix this by using the same check for folio_test_anon() in
> zap_nonpresent_ptes(). Also add a hmm-test case for this.
>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>

LGTM so:

Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

Cheers, Lorenzo

> Reported-by: Arsen Arsenović <aarsenovic@baylibre.com>
> Fixes: 999dad824c39e ("mm/shmem: persist uffd-wp bit across zapping for file-backed")
> Cc: stable@vger.kernel.org
> ---
>  mm/memory.c                            |  2 +-
>  tools/testing/selftests/mm/hmm-tests.c | 50 ++++++++++++++++++++++++++
>  2 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index c65e82c86fed..3f22a67a4d7f 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1750,7 +1750,7 @@ static inline int zap_nonpresent_ptes(struct mmu_gather *tlb,
>  		 * consider uffd-wp bit when zap. For more information,
>  		 * see zap_install_uffd_wp_if_needed().
>  		 */
> -		WARN_ON_ONCE(!vma_is_anonymous(vma));

I actually wonder if we should rename this to vma_is_pure_anon() or something to
make it clearer. But that'd be quite some churn, even for me :)

> +		WARN_ON_ONCE(!folio_test_anon(folio));
>  		rss[mm_counter(folio)]--;
>  		folio_remove_rmap_pte(folio, page, vma);
>  		folio_put(folio);
> diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftests/mm/hmm-tests.c
> index e8328c89d855..eb860b5d6f85 100644
> --- a/tools/testing/selftests/mm/hmm-tests.c
> +++ b/tools/testing/selftests/mm/hmm-tests.c
> @@ -1034,6 +1034,56 @@ TEST_F(hmm, migrate)
>  	hmm_buffer_free(buffer);
>  }
>
> +/*
> + * Migrate private file memory to device private memory.
> + */
> +TEST_F(hmm, migrate_file_private)
> +{
> +	struct hmm_buffer *buffer;
> +	unsigned long npages;
> +	unsigned long size;
> +	unsigned long i;
> +	int *ptr;
> +	int ret;
> +	int fd;
> +
> +	npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
> +	ASSERT_NE(npages, 0);
> +	size = npages << self->page_shift;
> +
> +	fd = hmm_create_file(size);
> +	ASSERT_GE(fd, 0);
> +
> +	buffer = malloc(sizeof(*buffer));
> +	ASSERT_NE(buffer, NULL);
> +
> +	buffer->fd = fd;
> +	buffer->size = size;
> +	buffer->mirror = malloc(size);
> +	ASSERT_NE(buffer->mirror, NULL);
> +
> +	buffer->ptr = mmap(NULL, size,
> +			   PROT_READ | PROT_WRITE,
> +			   MAP_PRIVATE,
> +			   buffer->fd, 0);
> +	ASSERT_NE(buffer->ptr, MAP_FAILED);
> +
> +	/* Initialize buffer in system memory. */
> +	for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
> +		ptr[i] = i;
> +
> +	/* Migrate memory to device. */
> +	ret = hmm_migrate_sys_to_dev(self->fd, buffer, npages);
> +	ASSERT_EQ(ret, 0);
> +	ASSERT_EQ(buffer->cpages, npages);
> +
> +	/* Check what the device read. */
> +	for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
> +		ASSERT_EQ(ptr[i], i);
> +
> +	hmm_buffer_free(buffer);
> +}
> +
>  /*
>   * Migrate anonymous memory to device private memory and fault some of it back
>   * to system memory, then try migrating the resulting mix of system and device
> --
> 2.54.0
>
>
>