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CVE-2026-98939— x86/mm: Drop unnecessary PMD page copy when freeing

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Linux 内核中，以下漏洞已被修复： x86/mm：在释放时移除不必要的 PMD 页副本 在配备独立显卡的系统上，一旦 kswapd 收缩 TTM 页面池，lockdep 便会立即报告潜在的死锁。直接原因是某条 x86 提交在内核页面属性修改代码中引入了 。 巨大的 vmap 代码在持有该锁的同时执行了 分配，这在回收（reclaim）过程也可能获取该锁的情况下是绝对禁止的。该分配发生在页表释放路径中，且其目的存疑 [1]。本质上，该代码试图避免硬件在硬件无法访问的页表条目中将 Accessed 标志置为 1

AI Predicted 5.5 Difficulty: Hard
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I. Basic Information for CVE-2026-98939

Vulnerability Information
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Vulnerability Title
x86/mm: Drop unnecessary PMD page copy when freeing
Source: CVE Program / CVE List V5
Vulnerability 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. ]
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux e21a9ea81426a85fdb0cdcfcc99d5d9c16b402ab ~ d3c2d2692bdf4af94bb27bc7a3aa0a348a567606 -
Linux Linux 6.18.53 ~ 6.18.56 -

II. Public POCs for CVE-2026-98939

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III. Intelligence Information for CVE-2026-98939

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Other References for CVE-2026-98939 (3)

Same Patch Batch · Linux · 2026-10-23 · 218 CVEs total

CVE-2026-98937 perf/core: Check kernel access when kernel callchains are requested
CVE-2026-98951 riscv: ptrace: Zero-initialize regset buffers before copyin
CVE-2026-98950 flow_dissector: avoid u16 truncation of hlen in bpf_flow_dissect()
CVE-2026-98949 drm/imagination: Fix reference and vm_bo handling in remap()
CVE-2026-98948 mlxsw: spectrum_flower: Fix port range register leak in tmplt_create()
CVE-2026-98947 vsock: Fix memory leak in vmci_transport_recv_dgram_cb()
CVE-2026-98946 drm/vc4: Disable the V3D interrupt across runtime suspend
CVE-2026-98945 HID: steam: Rearrange teardown sequence
CVE-2026-98944 HID: steam: Refactor registration
CVE-2026-98943 HID: steam: Clean up locking
CVE-2026-98942 sched_ext: Build the cid tables privately and publish them with RCU
CVE-2026-98941 ext4: don't enable large folios on encrypted inodes
CVE-2026-98940 ASoC: qcom: lpass-cpu: use DAI table index for playback constraints
CVE-2026-98938 rust: irq: pass RegistrationInner as cookie to request_irq
CVE-2026-98926 drm/amd/display: Remove sink usage from DPMS
CVE-2026-98929 macsec: initialize SecY before registering the netdevice
CVE-2026-98928 KVM: arm64: Derive GUEST_HAS_SVE from the SVE feature bit at EL2
CVE-2026-98927 KVM: arm64: nv: Fix life cycle of the nested_mmus array
CVE-2026-98930 KVM: s390: Fix IRQ injection with SIGP Stop and Store Status
CVE-2026-98925 bpf, sockmap: Fix self-redirect copied_seq double-counting

Showing top 20 of 218 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-98939

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