CVE-2026-98939 (GCVE-0-2026-98939)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:12 – Updated: 2026-10-23 12:12
VLAI
Title
x86/mm: Drop unnecessary PMD page copy when freeing
Summary
In the Linux kernel, the following vulnerability has been resolved: x86/mm: Drop unnecessary PMD page copy when freeing On a box with a discrete GPU, lockdep reports a possible deadlock as soon as kswapd shrinks the TTM page pool. The immediate cause is an x86 commit that added an mmap_read_lock() to kernel page protection munging code. The huge vmap code holds the same lock over a GFP_KERNEL allocation, which is a no-no now that reclaim can take it. That allocation is in a page table *free* path and ends up being for dubious purposes[1]. Basically, it tries to avoid hardware setting Accessed=1 in page table entries that are unreachable by the hardware, a non-issue. Remove the PMD copy. Detach the original PMD page at the PUD, flush the mid-level caches, and free the PTE tables straight from the detached PMD page. With no allocation left, the locking issue is gone. Lockdep splat/analysis: WARNING: possible circular locking dependency detected 7.3.0-rc3-f6e7b42bf05b+ #183 Tainted: G U ------------------------------------------------------ kswapd0/269 is trying to acquire lock: ((init_mm).mmap_lock){++++}-{4:4}, at: change_page_attr_set_clr+0x29a/0x4a0 but task is already holding lock: (pool_shrink_rwsem){.+.+}-{4:4}, at: ttm_pool_shrink+0xb2/0x330 [ttm] Chain exists of: (init_mm).mmap_lock --> fs_reclaim --> pool_shrink_rwsem The cycle is built from three edges: 1) pool_shrink_rwsem -> (init_mm).mmap_lock The TTM shrinker restores the caching attribute of every page it frees, while holding pool_shrink_rwsem: ttm_pool_shrink() -> ttm_pool_dispose_list() -> ttm_pool_free_page() -> set_pages_wb() -> change_page_attr_set_clr() [ init_mm mmap read lock ] 2) fs_reclaim -> pool_shrink_rwsem The same shrinker, called from reclaim. 3) (init_mm).mmap_lock -> fs_reclaim ioremap() installing a huge PUD mapping over an existing PMD table: ioremap_page_range() -> vmap_range_noflush() -> vmap_try_huge_pud() [ init_mm mmap read lock ] -> pud_free_pmd_page() -> __get_free_page(GFP_KERNEL) [ enters reclaim ] [ dhansen: Lots of changelog munging/trimming and merged comments from my version of the fix. ]
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6653 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: e21a9ea81426a85fdb0cdcfcc99d5d9c16b402ab , < d3c2d2692bdf4af94bb27bc7a3aa0a348a567606 (git)
Affected: cc73b2043d106b467accd38e9b1fc09e0607c056 , < f38c57a28ebbd057471573e39555d5aa11ab03cf (git)
Affected: d5d8b8662e6e5a565b47a0388640e88402f23274 , < e3ee38c1bc0b11a8d3e63dce7050759b61864286 (git)
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Linux Linux Affected: 6.18.53 , < 6.18.56 (semver)
Affected: 7.2.7 , < 7.2.10 (semver)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/mm/pgtable.c"
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      "cpeApplicability": [
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          "nodes": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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        {
          "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 --\u003e fs_reclaim --\u003e pool_shrink_rwsem\n\nThe cycle is built from three edges:\n\n  1) pool_shrink_rwsem -\u003e (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       -\u003e ttm_pool_dispose_list()\n       -\u003e ttm_pool_free_page()\n       -\u003e set_pages_wb()\n       -\u003e change_page_attr_set_clr()   [ init_mm mmap read lock ]\n\n  2) fs_reclaim -\u003e pool_shrink_rwsem\n\n     The same shrinker, called from reclaim.\n\n  3) (init_mm).mmap_lock -\u003e fs_reclaim\n\n     ioremap() installing a huge PUD mapping over an existing PMD table:\n\n       ioremap_page_range()\n       -\u003e vmap_range_noflush()\n       -\u003e vmap_try_huge_pud()          [ init_mm mmap read lock ]\n       -\u003e pud_free_pmd_page()\n       -\u003e __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"
      },
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        },
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          "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",
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    "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"
  },
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  "dataVersion": "5.2",
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      "date": "2026-11-08",
      "epss": "0.00166",
      "percentile": "0.05938"
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                "programFiles": [
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        "cveTags": [],
        "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 --\u003e fs_reclaim --\u003e pool_shrink_rwsem\n\nThe cycle is built from three edges:\n\n  1) pool_shrink_rwsem -\u003e (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       -\u003e ttm_pool_dispose_list()\n       -\u003e ttm_pool_free_page()\n       -\u003e set_pages_wb()\n       -\u003e change_page_attr_set_clr()   [ init_mm mmap read lock ]\n\n  2) fs_reclaim -\u003e pool_shrink_rwsem\n\n     The same shrinker, called from reclaim.\n\n  3) (init_mm).mmap_lock -\u003e fs_reclaim\n\n     ioremap() installing a huge PUD mapping over an existing PMD table:\n\n       ioremap_page_range()\n       -\u003e vmap_range_noflush()\n       -\u003e vmap_try_huge_pud()          [ init_mm mmap read lock ]\n       -\u003e pud_free_pmd_page()\n       -\u003e __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. ]"
          }
        ],
        "id": "CVE-2026-98939",
        "lastModified": "2026-10-23T13:17:14.843",
        "metrics": {},
        "published": "2026-10-23T13:17:14.843",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/d3c2d2692bdf4af94bb27bc7a3aa0a348a567606"
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        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-11-06T03:19:11+00:00",
      "cve": "CVE-2026-98939",
      "id": "CVE-2026-98939",
      "initial_release_date": "2026-10-23T12:12:06.180000+00:00",
      "product_status:known_affected": "203",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: kernel: Denial of Service via circular locking dependency during page freeing",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98939.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-11-04T17:47:57Z",
      "cve": "CVE-2026-98939",
      "id": "CVE-2026-98939",
      "initial_release_date": "2026-10-23T23:53:06Z",
      "product_status:known_not_affected": "348",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-98939",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2026/cve-2026-98939.json",
      "version": "5"
    }
  }
}



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