CVE-2026-98939

Full vulnerability record from the local CVENow database.

Description

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

Not scored

CVSS score

Not available

Vulnerability status

Received

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2026-10-23 13:17:14.843000

Last modified

2026-10-23 13:17:14.843000

View original CVE JSON

{
  "id": "CVE-2026-98939",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2026-10-23T13:17:14.843",
  "lastModified": "2026-10-23T13:17:14.843",
  "vulnStatus": "Received",
  "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 --> 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. ]"
    }
  ],
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "programFiles": [
            "arch/x86/mm/pgtable.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "e21a9ea81426a85fdb0cdcfcc99d5d9c16b402ab",
              "lessThan": "d3c2d2692bdf4af94bb27bc7a3aa0a348a567606",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "cc73b2043d106b467accd38e9b1fc09e0607c056",
              "lessThan": "f38c57a28ebbd057471573e39555d5aa11ab03cf",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "d5d8b8662e6e5a565b47a0388640e88402f23274",
              "lessThan": "e3ee38c1bc0b11a8d3e63dce7050759b61864286",
              "versionType": "git",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "programFiles": [
            "arch/x86/mm/pgtable.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "6.18.53",
              "lessThan": "6.18.56",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "7.2.7",
              "lessThan": "7.2.10",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {},
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/d3c2d2692bdf4af94bb27bc7a3aa0a348a567606",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/e3ee38c1bc0b11a8d3e63dce7050759b61864286",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/f38c57a28ebbd057471573e39555d5aa11ab03cf",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ]
}