{"api_version":"1","generated_at":"2026-10-28T06:16:05+00:00","cve":"CVE-2026-98939","urls":{"html":"https://cve.report/CVE-2026-98939","api":"https://cve.report/api/cve/CVE-2026-98939.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-98939","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-98939"},"summary":{"title":"x86/mm: Drop unnecessary PMD page copy when freeing","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm: Drop unnecessary PMD page copy when freeing\n\nOn a box with a discrete GPU, lockdep reports a possible deadlock as\nsoon as kswapd shrinks the TTM page pool. The immediate cause is an\nx86 commit that added an mmap_read_lock() to kernel page protection\nmunging code.\n\nThe huge vmap code holds the same lock over a GFP_KERNEL allocation,\nwhich is a no-no now that reclaim can take it. That allocation is in a\npage table *free* path and ends up being for dubious purposes[1].\nBasically, it tries to avoid hardware setting Accessed=1 in page table\nentries that are unreachable by the hardware, a non-issue.\n\nRemove the PMD copy. Detach the original PMD page at the PUD, flush\nthe mid-level caches, and free the PTE tables straight from the\ndetached PMD page. With no allocation left, the locking issue is gone.\n\nLockdep splat/analysis:\n\n  WARNING: possible circular locking dependency detected\n  7.3.0-rc3-f6e7b42bf05b+ #183 Tainted: G     U\n  ------------------------------------------------------\n  kswapd0/269 is trying to acquire lock:\n  ((init_mm).mmap_lock){++++}-{4:4}, at: change_page_attr_set_clr+0x29a/0x4a0\n  but task is already holding lock:\n  (pool_shrink_rwsem){.+.+}-{4:4}, at: ttm_pool_shrink+0xb2/0x330 [ttm]\n  Chain exists of:\n    (init_mm).mmap_lock --> fs_reclaim --> pool_shrink_rwsem\n\nThe cycle is built from three edges:\n\n  1) pool_shrink_rwsem -> (init_mm).mmap_lock\n\n     The TTM shrinker restores the caching attribute of every page it\n     frees, while holding pool_shrink_rwsem:\n\n       ttm_pool_shrink()\n       -> ttm_pool_dispose_list()\n       -> ttm_pool_free_page()\n       -> set_pages_wb()\n       -> change_page_attr_set_clr()   [ init_mm mmap read lock ]\n\n  2) fs_reclaim -> pool_shrink_rwsem\n\n     The same shrinker, called from reclaim.\n\n  3) (init_mm).mmap_lock -> fs_reclaim\n\n     ioremap() installing a huge PUD mapping over an existing PMD table:\n\n       ioremap_page_range()\n       -> vmap_range_noflush()\n       -> vmap_try_huge_pud()          [ init_mm mmap read lock ]\n       -> pud_free_pmd_page()\n       -> __get_free_page(GFP_KERNEL)  [ enters reclaim ]\n\n[ dhansen: Lots of changelog munging/trimming and merged comments from my\n\t   version of the fix. ]","state":"PUBLISHED","assigner":"Linux","published_at":"2026-10-23 13:17:14","updated_at":"2026-10-23 13:17:14"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/e3ee38c1bc0b11a8d3e63dce7050759b61864286","name":"https://git.kernel.org/stable/c/e3ee38c1bc0b11a8d3e63dce7050759b61864286","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/d3c2d2692bdf4af94bb27bc7a3aa0a348a567606","name":"https://git.kernel.org/stable/c/d3c2d2692bdf4af94bb27bc7a3aa0a348a567606","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/f38c57a28ebbd057471573e39555d5aa11ab03cf","name":"https://git.kernel.org/stable/c/f38c57a28ebbd057471573e39555d5aa11ab03cf","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-98939","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98939","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected e21a9ea81426a85fdb0cdcfcc99d5d9c16b402ab d3c2d2692bdf4af94bb27bc7a3aa0a348a567606 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected cc73b2043d106b467accd38e9b1fc09e0607c056 f38c57a28ebbd057471573e39555d5aa11ab03cf git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected d5d8b8662e6e5a565b47a0388640e88402f23274 e3ee38c1bc0b11a8d3e63dce7050759b61864286 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.18.53 6.18.56 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 7.2.7 7.2.10 semver","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["arch/x86/mm/pgtable.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"d3c2d2692bdf4af94bb27bc7a3aa0a348a567606","status":"affected","version":"e21a9ea81426a85fdb0cdcfcc99d5d9c16b402ab","versionType":"git"},{"lessThan":"f38c57a28ebbd057471573e39555d5aa11ab03cf","status":"affected","version":"cc73b2043d106b467accd38e9b1fc09e0607c056","versionType":"git"},{"lessThan":"e3ee38c1bc0b11a8d3e63dce7050759b61864286","status":"affected","version":"d5d8b8662e6e5a565b47a0388640e88402f23274","versionType":"git"}]},{"defaultStatus":"unaffected","product":"Linux","programFiles":["arch/x86/mm/pgtable.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"6.18.56","status":"affected","version":"6.18.53","versionType":"semver"},{"lessThan":"7.2.10","status":"affected","version":"7.2.7","versionType":"semver"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.56","versionStartIncluding":"6.18.53","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2.10","versionStartIncluding":"7.2.7","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm: Drop unnecessary PMD page copy when freeing\n\nOn a box with a discrete GPU, lockdep reports a possible deadlock as\nsoon as kswapd shrinks the TTM page pool. The immediate cause is an\nx86 commit that added an mmap_read_lock() to kernel page protection\nmunging code.\n\nThe huge vmap code holds the same lock over a GFP_KERNEL allocation,\nwhich is a no-no now that reclaim can take it. That allocation is in a\npage table *free* path and ends up being for dubious purposes[1].\nBasically, it tries to avoid hardware setting Accessed=1 in page table\nentries that are unreachable by the hardware, a non-issue.\n\nRemove the PMD copy. Detach the original PMD page at the PUD, flush\nthe mid-level caches, and free the PTE tables straight from the\ndetached PMD page. With no allocation left, the locking issue is gone.\n\nLockdep splat/analysis:\n\n  WARNING: possible circular locking dependency detected\n  7.3.0-rc3-f6e7b42bf05b+ #183 Tainted: G     U\n  ------------------------------------------------------\n  kswapd0/269 is trying to acquire lock:\n  ((init_mm).mmap_lock){++++}-{4:4}, at: change_page_attr_set_clr+0x29a/0x4a0\n  but task is already holding lock:\n  (pool_shrink_rwsem){.+.+}-{4:4}, at: ttm_pool_shrink+0xb2/0x330 [ttm]\n  Chain exists of:\n    (init_mm).mmap_lock --> fs_reclaim --> pool_shrink_rwsem\n\nThe cycle is built from three edges:\n\n  1) pool_shrink_rwsem -> (init_mm).mmap_lock\n\n     The TTM shrinker restores the caching attribute of every page it\n     frees, while holding pool_shrink_rwsem:\n\n       ttm_pool_shrink()\n       -> ttm_pool_dispose_list()\n       -> ttm_pool_free_page()\n       -> set_pages_wb()\n       -> change_page_attr_set_clr()   [ init_mm mmap read lock ]\n\n  2) fs_reclaim -> pool_shrink_rwsem\n\n     The same shrinker, called from reclaim.\n\n  3) (init_mm).mmap_lock -> fs_reclaim\n\n     ioremap() installing a huge PUD mapping over an existing PMD table:\n\n       ioremap_page_range()\n       -> vmap_range_noflush()\n       -> vmap_try_huge_pud()          [ init_mm mmap read lock ]\n       -> pud_free_pmd_page()\n       -> __get_free_page(GFP_KERNEL)  [ enters reclaim ]\n\n[ dhansen: Lots of changelog munging/trimming and merged comments from my\n\t   version of the fix. ]"}],"providerMetadata":{"dateUpdated":"2026-10-23T12:12:06.180Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/d3c2d2692bdf4af94bb27bc7a3aa0a348a567606"},{"url":"https://git.kernel.org/stable/c/f38c57a28ebbd057471573e39555d5aa11ab03cf"},{"url":"https://git.kernel.org/stable/c/e3ee38c1bc0b11a8d3e63dce7050759b61864286"}],"title":"x86/mm: Drop unnecessary PMD page copy when freeing","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-98939","datePublished":"2026-10-23T12:12:06.180Z","dateReserved":"2026-09-25T10:25:14.381Z","dateUpdated":"2026-10-23T12:12:06.180Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-10-23 13:17:14","lastModifiedDate":"2026-10-23 13:17:14","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"98939","Ordinal":"1","Title":"x86/mm: Drop unnecessary PMD page copy when freeing","CVE":"CVE-2026-98939","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"98939","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm: Drop unnecessary PMD page copy when freeing\n\nOn a box with a discrete GPU, lockdep reports a possible deadlock as\nsoon as kswapd shrinks the TTM page pool. The immediate cause is an\nx86 commit that added an mmap_read_lock() to kernel page protection\nmunging code.\n\nThe huge vmap code holds the same lock over a GFP_KERNEL allocation,\nwhich is a no-no now that reclaim can take it. That allocation is in a\npage table *free* path and ends up being for dubious purposes[1].\nBasically, it tries to avoid hardware setting Accessed=1 in page table\nentries that are unreachable by the hardware, a non-issue.\n\nRemove the PMD copy. Detach the original PMD page at the PUD, flush\nthe mid-level caches, and free the PTE tables straight from the\ndetached PMD page. With no allocation left, the locking issue is gone.\n\nLockdep splat/analysis:\n\n  WARNING: possible circular locking dependency detected\n  7.3.0-rc3-f6e7b42bf05b+ #183 Tainted: G     U\n  ------------------------------------------------------\n  kswapd0/269 is trying to acquire lock:\n  ((init_mm).mmap_lock){++++}-{4:4}, at: change_page_attr_set_clr+0x29a/0x4a0\n  but task is already holding lock:\n  (pool_shrink_rwsem){.+.+}-{4:4}, at: ttm_pool_shrink+0xb2/0x330 [ttm]\n  Chain exists of:\n    (init_mm).mmap_lock --> fs_reclaim --> pool_shrink_rwsem\n\nThe cycle is built from three edges:\n\n  1) pool_shrink_rwsem -> (init_mm).mmap_lock\n\n     The TTM shrinker restores the caching attribute of every page it\n     frees, while holding pool_shrink_rwsem:\n\n       ttm_pool_shrink()\n       -> ttm_pool_dispose_list()\n       -> ttm_pool_free_page()\n       -> set_pages_wb()\n       -> change_page_attr_set_clr()   [ init_mm mmap read lock ]\n\n  2) fs_reclaim -> pool_shrink_rwsem\n\n     The same shrinker, called from reclaim.\n\n  3) (init_mm).mmap_lock -> fs_reclaim\n\n     ioremap() installing a huge PUD mapping over an existing PMD table:\n\n       ioremap_page_range()\n       -> vmap_range_noflush()\n       -> vmap_try_huge_pud()          [ init_mm mmap read lock ]\n       -> pud_free_pmd_page()\n       -> __get_free_page(GFP_KERNEL)  [ enters reclaim ]\n\n[ dhansen: Lots of changelog munging/trimming and merged comments from my\n\t   version of the fix. ]","Type":"Description","Title":"x86/mm: Drop unnecessary PMD page copy when freeing"}]}}}