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charset="utf-8" When dmirror_fops_release() is called it frees the dmirror struct but doesn't migrate device private pages back to system memory first. This leaves those pages with a dangling zone_device_data pointer to the freed dmirror. If a subsequent fault occurs on those pages (eg. during coredump) the dmirror_devmem_fault() callback dereferences the stale pointer causing a kernel panic. This was reported [1] when running mm/ksft_hmm.sh on arm64, where a test failure triggered SIGABRT and the resulting coredump walked the VMAs faulting in the stale device private pages. Fix this by calling dmirror_device_evict_chunk() for each devmem chunk in dmirror_fops_release() to migrate all device private pages back to system memory before freeing the dmirror struct. The function is moved earlier in the file to avoid a forward declaration. Fixes: b2ef9f5a5cb3 ("mm/hmm/test: add selftest driver for HMM") Reported-by: Zenghui Yu Closes: https://lore.kernel.org/linux-mm/8bd0396a-8997-4d2e-a13f-5aac033083= d7@linux.dev/ Signed-off-by: Alistair Popple Reviewed-by: Balbir Singh --- Note that I wasn't able to replicate the exact crash in [1] although I replicated something similar. So I haven't been able to verify this fixes the crash conclusively, but it should. [1] https://lore.kernel.org/linux-mm/8bd0396a-8997-4d2e-a13f-5aac033083d7@l= inux.dev/ --- lib/test_hmm.c | 112 +++++++++++++++++++++++++++---------------------- 1 file changed, 62 insertions(+), 50 deletions(-) diff --git a/lib/test_hmm.c b/lib/test_hmm.c index 0964d53365e6..79fe7d233df1 100644 --- a/lib/test_hmm.c +++ b/lib/test_hmm.c @@ -185,11 +185,73 @@ static int dmirror_fops_open(struct inode *inode, str= uct file *filp) return 0; } =20 +static void dmirror_device_evict_chunk(struct dmirror_chunk *chunk) +{ + unsigned long start_pfn =3D chunk->pagemap.range.start >> PAGE_SHIFT; + unsigned long end_pfn =3D chunk->pagemap.range.end >> PAGE_SHIFT; + unsigned long npages =3D end_pfn - start_pfn + 1; + unsigned long i; + unsigned long *src_pfns; + unsigned long *dst_pfns; + unsigned int order =3D 0; + + src_pfns =3D kvcalloc(npages, sizeof(*src_pfns), GFP_KERNEL | __GFP_NOFAI= L); + dst_pfns =3D kvcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL | __GFP_NOFAI= L); + + migrate_device_range(src_pfns, start_pfn, npages); + for (i =3D 0; i < npages; i++) { + struct page *dpage, *spage; + + spage =3D migrate_pfn_to_page(src_pfns[i]); + if (!spage || !(src_pfns[i] & MIGRATE_PFN_MIGRATE)) + continue; + + if (WARN_ON(!is_device_private_page(spage) && + !is_device_coherent_page(spage))) + continue; + + order =3D folio_order(page_folio(spage)); + spage =3D BACKING_PAGE(spage); + if (src_pfns[i] & MIGRATE_PFN_COMPOUND) { + dpage =3D folio_page(folio_alloc(GFP_HIGHUSER_MOVABLE, + order), 0); + } else { + dpage =3D alloc_page(GFP_HIGHUSER_MOVABLE | __GFP_NOFAIL); + order =3D 0; + } + + /* TODO Support splitting here */ + lock_page(dpage); + dst_pfns[i] =3D migrate_pfn(page_to_pfn(dpage)); + if (src_pfns[i] & MIGRATE_PFN_WRITE) + dst_pfns[i] |=3D MIGRATE_PFN_WRITE; + if (order) + dst_pfns[i] |=3D MIGRATE_PFN_COMPOUND; + folio_copy(page_folio(dpage), page_folio(spage)); + } + migrate_device_pages(src_pfns, dst_pfns, npages); + migrate_device_finalize(src_pfns, dst_pfns, npages); + kvfree(src_pfns); + kvfree(dst_pfns); +} + static int dmirror_fops_release(struct inode *inode, struct file *filp) { struct dmirror *dmirror =3D filp->private_data; + struct dmirror_device *mdevice =3D dmirror->mdevice; + int i; =20 mmu_interval_notifier_remove(&dmirror->notifier); + + if (mdevice->devmem_chunks) { + for (i =3D 0; i < mdevice->devmem_count; i++) { + struct dmirror_chunk *devmem =3D + mdevice->devmem_chunks[i]; + + dmirror_device_evict_chunk(devmem); + } + } + xa_destroy(&dmirror->pt); kfree(dmirror); return 0; @@ -1377,56 +1439,6 @@ static int dmirror_snapshot(struct dmirror *dmirror, return ret; } =20 -static void dmirror_device_evict_chunk(struct dmirror_chunk *chunk) -{ - unsigned long start_pfn =3D chunk->pagemap.range.start >> PAGE_SHIFT; - unsigned long end_pfn =3D chunk->pagemap.range.end >> PAGE_SHIFT; - unsigned long npages =3D end_pfn - start_pfn + 1; - unsigned long i; - unsigned long *src_pfns; - unsigned long *dst_pfns; - unsigned int order =3D 0; - - src_pfns =3D kvcalloc(npages, sizeof(*src_pfns), GFP_KERNEL | __GFP_NOFAI= L); - dst_pfns =3D kvcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL | __GFP_NOFAI= L); - - migrate_device_range(src_pfns, start_pfn, npages); - for (i =3D 0; i < npages; i++) { - struct page *dpage, *spage; - - spage =3D migrate_pfn_to_page(src_pfns[i]); - if (!spage || !(src_pfns[i] & MIGRATE_PFN_MIGRATE)) - continue; - - if (WARN_ON(!is_device_private_page(spage) && - !is_device_coherent_page(spage))) - continue; - - order =3D folio_order(page_folio(spage)); - spage =3D BACKING_PAGE(spage); - if (src_pfns[i] & MIGRATE_PFN_COMPOUND) { - dpage =3D folio_page(folio_alloc(GFP_HIGHUSER_MOVABLE, - order), 0); - } else { - dpage =3D alloc_page(GFP_HIGHUSER_MOVABLE | __GFP_NOFAIL); - order =3D 0; - } - - /* TODO Support splitting here */ - lock_page(dpage); - dst_pfns[i] =3D migrate_pfn(page_to_pfn(dpage)); - if (src_pfns[i] & MIGRATE_PFN_WRITE) - dst_pfns[i] |=3D MIGRATE_PFN_WRITE; - if (order) - dst_pfns[i] |=3D MIGRATE_PFN_COMPOUND; - folio_copy(page_folio(dpage), page_folio(spage)); - } - migrate_device_pages(src_pfns, dst_pfns, npages); 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Tue, 31 Mar 2026 06:35:03 +0000 Received: from DS0PR12MB7726.namprd12.prod.outlook.com ([fe80::5807:8e24:69b0:f6c0]) by DS0PR12MB7726.namprd12.prod.outlook.com ([fe80::5807:8e24:69b0:f6c0%4]) with mapi id 15.20.9769.014; Tue, 31 Mar 2026 06:35:03 +0000 From: Alistair Popple To: linux-mm@kvack.org Cc: zenghui.yu@linux.dev, Liam.Howlett@oracle.com, akpm@linux-foundation.org, david@kernel.org, jgg@ziepe.ca, leon@kernel.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@suse.com, rppt@kernel.org, surenb@google.com, vbabka@kernel.org, dri-devel@lists.freedesktop.org, balbirs@nvidia.com, Alistair Popple Subject: [PATCH 2/3] selftests/mm: hmm-tests: don't hardcode THP size to 2MB Date: Tue, 31 Mar 2026 17:34:44 +1100 Message-ID: <20260331063445.3551404-3-apopple@nvidia.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260331063445.3551404-1-apopple@nvidia.com> References: <20260331063445.3551404-1-apopple@nvidia.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: SY5P282CA0153.AUSP282.PROD.OUTLOOK.COM (2603:10c6:10:24a::13) To DS0PR12MB7726.namprd12.prod.outlook.com (2603:10b6:8:130::6) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR12MB7726:EE_|MN0PR12MB6150:EE_ X-MS-Office365-Filtering-Correlation-Id: 1e22adf9-5d28-42b5-d837-08de8eefa421 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024|13003099007|18002099003|22082099003|56012099003; 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charset="utf-8" Several HMM tests hardcode TWOMEG as the THP size. This is wrong on architectures where the PMD size is not 2MB such as arm64 with 64K base pages where THP is 512MB. Fix this by using read_pmd_pagesize() from vm_util instead. While here also replace the custom file_read_ulong() helper used to parse the default hugetlbfs page size from /proc/meminfo with the existing default_huge_page_size() from vm_util. [1] https://lore.kernel.org/linux-mm/8bd0396a-8997-4d2e-a13f-5aac033083d7@l= inux.dev/ Fixes: fee9f6d1b8df ("mm/hmm/test: add selftests for HMM") Fixes: 519071529d2a ("selftests/mm/hmm-tests: new tests for zone device THP= migration") Reported-by: Zenghui Yu Closes: https://lore.kernel.org/linux-mm/8bd0396a-8997-4d2e-a13f-5aac033083= d7@linux.dev/ Signed-off-by: Alistair Popple Reviewed-by: Balbir Singh --- tools/testing/selftests/mm/hmm-tests.c | 83 +++++--------------------- 1 file changed, 16 insertions(+), 67 deletions(-) diff --git a/tools/testing/selftests/mm/hmm-tests.c b/tools/testing/selftes= ts/mm/hmm-tests.c index e8328c89d855..788689497e92 100644 --- a/tools/testing/selftests/mm/hmm-tests.c +++ b/tools/testing/selftests/mm/hmm-tests.c @@ -34,6 +34,7 @@ */ #include #include +#include =20 struct hmm_buffer { void *ptr; @@ -548,7 +549,7 @@ TEST_F(hmm, anon_write_child) =20 for (migrate =3D 0; migrate < 2; ++migrate) { for (use_thp =3D 0; use_thp < 2; ++use_thp) { - npages =3D ALIGN(use_thp ? TWOMEG : HMM_BUFFER_SIZE, + npages =3D ALIGN(use_thp ? read_pmd_pagesize() : HMM_BUFFER_SIZE, self->page_size) >> self->page_shift; ASSERT_NE(npages, 0); size =3D npages << self->page_shift; @@ -728,7 +729,7 @@ TEST_F(hmm, anon_write_huge) int *ptr; int ret; =20 - size =3D 2 * TWOMEG; + size =3D 2 * read_pmd_pagesize(); =20 buffer =3D malloc(sizeof(*buffer)); ASSERT_NE(buffer, NULL); @@ -744,7 +745,7 @@ TEST_F(hmm, anon_write_huge) buffer->fd, 0); ASSERT_NE(buffer->ptr, MAP_FAILED); =20 - size =3D TWOMEG; + size /=3D 2; npages =3D size >> self->page_shift; map =3D (void *)ALIGN((uintptr_t)buffer->ptr, size); ret =3D madvise(map, size, MADV_HUGEPAGE); @@ -770,54 +771,6 @@ TEST_F(hmm, anon_write_huge) hmm_buffer_free(buffer); } =20 -/* - * Read numeric data from raw and tagged kernel status files. Used to read - * /proc and /sys data (without a tag) and from /proc/meminfo (with a tag). - */ -static long file_read_ulong(char *file, const char *tag) -{ - int fd; - char buf[2048]; - int len; - char *p, *q; - long val; - - fd =3D open(file, O_RDONLY); - if (fd < 0) { - /* Error opening the file */ - return -1; - } - - len =3D read(fd, buf, sizeof(buf)); - close(fd); - if (len < 0) { - /* Error in reading the file */ - return -1; - } - if (len =3D=3D sizeof(buf)) { - /* Error file is too large */ - return -1; - } - buf[len] =3D '\0'; - - /* Search for a tag if provided */ - if (tag) { - p =3D strstr(buf, tag); - if (!p) - return -1; /* looks like the line we want isn't there */ - p +=3D strlen(tag); - } else - p =3D buf; - - val =3D strtol(p, &q, 0); - if (*q !=3D ' ') { - /* Error parsing the file */ - return -1; - } - - return val; -} - /* * Write huge TLBFS page. */ @@ -826,15 +779,13 @@ TEST_F(hmm, anon_write_hugetlbfs) struct hmm_buffer *buffer; unsigned long npages; unsigned long size; - unsigned long default_hsize; + unsigned long default_hsize =3D default_huge_page_size(); unsigned long i; int *ptr; int ret; =20 - default_hsize =3D file_read_ulong("/proc/meminfo", "Hugepagesize:"); - if (default_hsize < 0 || default_hsize*1024 < default_hsize) + if (!default_hsize) SKIP(return, "Huge page size could not be determined"); - default_hsize =3D default_hsize*1024; /* KB to B */ =20 size =3D ALIGN(TWOMEG, default_hsize); npages =3D size >> self->page_shift; @@ -1606,7 +1557,7 @@ TEST_F(hmm, compound) struct hmm_buffer *buffer; unsigned long npages; unsigned long size; - unsigned long default_hsize; + unsigned long default_hsize =3D default_huge_page_size(); int *ptr; unsigned char *m; int ret; @@ -1614,10 +1565,8 @@ TEST_F(hmm, compound) =20 /* Skip test if we can't allocate a hugetlbfs page. */ =20 - default_hsize =3D file_read_ulong("/proc/meminfo", "Hugepagesize:"); - if (default_hsize < 0 || default_hsize*1024 < default_hsize) + if (!default_hsize) SKIP(return, "Huge page size could not be determined"); - default_hsize =3D default_hsize*1024; /* KB to B */ =20 size =3D ALIGN(TWOMEG, default_hsize); npages =3D size >> self->page_shift; @@ -2106,7 +2055,7 @@ TEST_F(hmm, migrate_anon_huge_empty) int *ptr; int ret; =20 - size =3D TWOMEG; + size =3D read_pmd_pagesize(); =20 buffer =3D malloc(sizeof(*buffer)); ASSERT_NE(buffer, NULL); @@ -2158,7 +2107,7 @@ TEST_F(hmm, migrate_anon_huge_zero) int ret; int val; =20 - size =3D TWOMEG; + size =3D read_pmd_pagesize(); =20 buffer =3D malloc(sizeof(*buffer)); ASSERT_NE(buffer, NULL); @@ -2221,7 +2170,7 @@ TEST_F(hmm, migrate_anon_huge_free) int *ptr; int ret; =20 - size =3D TWOMEG; + size =3D read_pmd_pagesize(); =20 buffer =3D malloc(sizeof(*buffer)); ASSERT_NE(buffer, NULL); @@ -2280,7 +2229,7 @@ TEST_F(hmm, migrate_anon_huge_fault) int *ptr; int ret; =20 - size =3D TWOMEG; + size =3D read_pmd_pagesize(); =20 buffer =3D malloc(sizeof(*buffer)); ASSERT_NE(buffer, NULL); @@ -2332,7 +2281,7 @@ TEST_F(hmm, migrate_partial_unmap_fault) { struct hmm_buffer *buffer; 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charset="utf-8" Unloading the HMM test module produces the following warning: [ 3782.224783] ------------[ cut here ]------------ [ 3782.226323] Device 'hmm_dmirror0' does not have a release() function, it= is broken and must be fixed. See Documentation/core-api/kobject.rst. [ 3782.230570] WARNING: drivers/base/core.c:2567 at device_release+0x185/0x= 210, CPU#20: rmmod/1924 [ 3782.233949] Modules linked in: test_hmm(-) nvidia_uvm(O) nvidia(O) [ 3782.236321] CPU: 20 UID: 0 PID: 1924 Comm: rmmod Tainted: G O = 7.0.0-rc1+ #374 PREEMPT(full) [ 3782.240226] Tainted: [O]=3DOOT_MODULE [ 3782.241639] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel= -1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 [ 3782.246193] RIP: 0010:device_release+0x185/0x210 [ 3782.247860] Code: 00 00 fc ff df 48 8d 7b 50 48 89 fa 48 c1 ea 03 80 3c = 02 00 0f 85 86 00 00 00 48 8b 73 50 48 85 f6 74 11 48 8d 3d db 25 29 03 <67= > 48 0f b9 3a e9 0d ff ff ff 48 b8 00 00 00 00 00 fc ff df 48 89 [ 3782.254211] RSP: 0018:ffff888126577d98 EFLAGS: 00010246 [ 3782.256054] RAX: dffffc0000000000 RBX: ffffffffc2b70310 RCX: ffffffff8fe= 61ba1 [ 3782.258512] RDX: 1ffffffff856e062 RSI: ffff88811341eea0 RDI: ffffffff91b= bacb0 [ 3782.261041] RBP: ffff888111475000 R08: 0000000000000001 R09: fffffbfff85= 6e069 [ 3782.263471] R10: ffffffffc2b7034b R11: 00000000ffffffff R12: 00000000000= 00000 [ 3782.265983] R13: dffffc0000000000 R14: ffff88811341eea0 R15: 00000000000= 00000 [ 3782.268443] FS: 00007fd5a3689040(0000) GS:ffff88842c8d0000(0000) knlGS:= 0000000000000000 [ 3782.271236] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 3782.273251] CR2: 00007fd5a36d2c10 CR3: 00000001242b8000 CR4: 00000000000= 006f0 [ 3782.275362] Call Trace: [ 3782.276071] [ 3782.276678] kobject_put+0x146/0x270 [ 3782.277731] hmm_dmirror_exit+0x7a/0x130 [test_hmm] [ 3782.279135] __do_sys_delete_module+0x341/0x510 [ 3782.280438] ? module_flags+0x300/0x300 [ 3782.281547] do_syscall_64+0x111/0x670 [ 3782.282620] entry_SYSCALL_64_after_hwframe+0x4b/0x53 [ 3782.284091] RIP: 0033:0x7fd5a3793b37 [ 3782.285303] Code: 73 01 c3 48 8b 0d c9 82 0c 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 b0 00 00 00 0f 05 <48= > 3d 01 f0 ff ff 73 01 c3 48 8b 0d 99 82 0c 00 f7 d8 64 89 01 48 [ 3782.290708] RSP: 002b:00007ffd68b7dc68 EFLAGS: 00000206 ORIG_RAX: 000000= 00000000b0 [ 3782.292817] RAX: ffffffffffffffda RBX: 000055e3c0d1c770 RCX: 00007fd5a37= 93b37 [ 3782.294735] RDX: 0000000000000000 RSI: 0000000000000800 RDI: 000055e3c0d= 1c7d8 [ 3782.296661] RBP: 0000000000000000 R08: 1999999999999999 R09: 00000000000= 00000 [ 3782.298622] R10: 00007fd5a3806ac0 R11: 0000000000000206 R12: 00007ffd68b= 7deb0 [ 3782.300576] R13: 00007ffd68b7e781 R14: 000055e3c0d1b2a0 R15: 00007ffd68b= 7deb8 [ 3782.301963] [ 3782.302371] irq event stamp: 5019 [ 3782.302987] hardirqs last enabled at (5027): [] __up_= console_sem+0x52/0x60 [ 3782.304507] hardirqs last disabled at (5036): [] __up_= console_sem+0x37/0x60 [ 3782.306086] softirqs last enabled at (4940): [] __irq= _exit_rcu+0xc0/0xf0 [ 3782.307567] softirqs last disabled at (4929): [] __irq= _exit_rcu+0xc0/0xf0 [ 3782.309105] ---[ end trace 0000000000000000 ]--- This is because the test module doesn't have a device.release method. In this case one probably isn't needed for correctness - the device structs are in a static array so don't need freeing when the final reference goes away. However some device state is freed on exit, so to ensure this happens at the right time and to silence the warning move the deinitialisation to a release method and assign that as the device release callback. Whilst here also fix a minor error handling bug where cdev_device_del() wasn't being called if allocation failed. Signed-off-by: Alistair Popple Acked-by: Balbir Singh --- lib/test_hmm.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/lib/test_hmm.c b/lib/test_hmm.c index 79fe7d233df1..213504915737 100644 --- a/lib/test_hmm.c +++ b/lib/test_hmm.c @@ -1738,6 +1738,13 @@ static const struct dev_pagemap_ops dmirror_devmem_o= ps =3D { .folio_split =3D dmirror_devmem_folio_split, }; =20 +static void dmirror_device_release(struct device *dev) +{ + struct dmirror_device *mdevice =3D container_of(dev, struct dmirror_devic= e, device); + + dmirror_device_remove_chunks(mdevice); +} + static int dmirror_device_init(struct dmirror_device *mdevice, int id) { dev_t dev; @@ -1749,6 +1756,8 @@ static int dmirror_device_init(struct dmirror_device = *mdevice, int id) =20 cdev_init(&mdevice->cdevice, &dmirror_fops); mdevice->cdevice.owner =3D THIS_MODULE; + mdevice->device.release =3D dmirror_device_release; + device_initialize(&mdevice->device); mdevice->device.devt =3D dev; =20 @@ -1756,12 +1765,16 @@ static int dmirror_device_init(struct dmirror_devic= e *mdevice, int id) if (ret) goto put_device; =20 + /* Build a list of free ZONE_DEVICE struct pages */ + ret =3D dmirror_allocate_chunk(mdevice, NULL, false); + if (ret) + goto put_device; + ret =3D cdev_device_add(&mdevice->cdevice, &mdevice->device); if (ret) goto put_device; =20 - /* Build a list of free ZONE_DEVICE struct pages */ - return dmirror_allocate_chunk(mdevice, NULL, false); + return 0; =20 put_device: put_device(&mdevice->device); @@ -1770,7 +1783,6 @@ static int dmirror_device_init(struct dmirror_device = *mdevice, int id) =20 static void dmirror_device_remove(struct dmirror_device *mdevice) { - dmirror_device_remove_chunks(mdevice); cdev_device_del(&mdevice->cdevice, &mdevice->device); put_device(&mdevice->device); } --=20 2.53.0