{"id":"CVE-2026-98468","summary":"KVM: arm64: Fix spurious warning for benign stage 2 teardown race","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: arm64: Fix spurious warning for benign stage 2 teardown race\n\nkvmtool was used to establish an L1 guest with 8 CPUs and 8 GiB of RAM, an\nL2 guest with 4 CPUs and 4 GiB of RAM and an L3 guest with 2 CPUs and 2 GiB\nof RAM, all of which was then exited.\n\nUnder memory pressure in the L0 host warnings were observed due to\nmigration triggered by compaction:\n\nWARNING: arch/arm64/kvm/mmu.c:336 at __unmap_stage2_range+0x64/0x80,\nCPU#5: kcompactd0/66\n\nWhich was, in turn, triggered by an MMU notifier for the host invalidation:\n\nmmu_notifier_invalidate_range_start()\n  -\u003e ... -\u003e kvm_mmu_notifier_invalidate_range_start()\n    -\u003e kvm_mmu_unmap_gfn_range()\n      -\u003e kvm_unmap_gfn_range()\n        -\u003e kvm_nested_s2_unmap()\n          -\u003e kvm_stage2_unmap_range()\n            -\u003e __unmap_stage2_range()\n               -\u003e stage2_apply_range()\n       \t       \u003c- -EINVAL, triggering a WARN_ON()\n\nRacing with L0's teardown of stage 2 page tables:\n\nexit_mm()\n  -\u003e mmput()\n    -\u003e __mmput()\n      -\u003e exit_mmap()\n        -\u003e mmu_notifier_release()\n\t  -\u003e ... -\u003e kvm_mmu_notifier_release()\n            -\u003e kvm_flush_shadow_all()\n              -\u003e kvm_arch_flush_shadow_all()\n\t        -\u003e kvm_free_stage2_pgd()\n\t\t  -\u003e [ acquire kvm-\u003emmu_lock for write ]\n\t\t  -\u003e mmu-\u003epgt = NULL [ among other tasks ]\n\t\t  -\u003e [ release kvm-\u003emmu_lock for write ]\n\nIt turns out there is a benign race resulting in a spurious warning:\n\n\tThread A - notify: migration   | Thread B - notify: release\n\t-------------------------------|---------------------------------\n\t\u003c kvm-\u003emmu_lock held \u003e         |\n\tstage2_apply_range()           |\n\t  get mmu-\u003epgt, check !NULL    |\n\t  ...                          | kvm_arch_flush_shadow_all()\n\t  cond_resched_rwlock_write(); |   \u003c contend, sleep kvm-\u003emmu_lock \u003e\n\t\u003c drop kvm-\u003emmu_lock \u003e         |   \u003c acquire kvm-\u003emmu_lock\u003e\n                                       |   ...\n\t\t\t\t       |   kvm_free_stage2_pgd()\n                                       |     mmu-\u003epgt = NULL\n\t\t\t\t       |   \u003c invalidate MMU \u003e\n\t\t\t\t       |   ...\n\t\t\t\t       |   \u003c release kvm-\u003emmu_lock \u003e\n\t[ scheduled ]\t\t       |\n\tstage2_apply_range()           |\n\t  \u003c loop to next \u003e             |\n\t  get, mmu-\u003epgt, check !NULL   |\n\t  is NULL, return -EINVAL      |\n        __unmap_stage2_range()         |\n\t  WARN_ON(-EINVAL) \u003c--- entirely spurious - the race was handled\n                                 correctly.\n\nFix the spurious warning by updating stage2_apply_range() to no longer\ntreat concurrent PGT teardown on lock release as an error - whether the\nwalker is tearing down page tables or doing something else this is a\nlegitimate reason to abort the operation without error.\n\nThis keeps the warning in place for all other circumstances.\n\nIn practice only __unmap_stage2_range() actually does anything with the\nerror so this only impacts that.","modified":"2026-10-20T02:31:05.795547747Z","published":"2026-10-18T15:15:20.882Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98468.json"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/330346dda3bf5f8a3b06723024f7d906326270cf"},{"type":"WEB","url":"https://git.kernel.org/stable/c/38b70fc453c3112f1a62583b89903ae41116cc27"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c23ed110d27ba99cf3a881986514f79aacedf476"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f44a92633136b409ebb9b7036fceb7e11de60a20"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98468.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98468"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"ec14c272408af43d392f65f55e66f3b94fc61921"},{"fixed":"f44a92633136b409ebb9b7036fceb7e11de60a20"},{"fixed":"c23ed110d27ba99cf3a881986514f79aacedf476"},{"fixed":"330346dda3bf5f8a3b06723024f7d906326270cf"},{"fixed":"38b70fc453c3112f1a62583b89903ae41116cc27"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98468.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.11.0"},{"fixed":"6.12.112"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.55"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.9"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98468.json"}}],"schema_version":"1.9.0"}