{"id":"CVE-2026-89756","state":"PUBLISHED","title":"mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()\n\nmigrate_pages_batch() unmaps each folio before moving it, and every\nunmap runs the mmu_notifier invalidate callbacks.  On KVM hosts\ntry_to_migrate() ends up in kvm_mmu_notifier_invalidate_range_start() ->\ntdp_mmu_zap_leafs(), which is expensive, so unmapping a large batch keeps\nthe CPU busy for a long time.\n\nThe loop already calls cond_resched(), but on PREEMPTION kernels that is\na no-op, and involuntary preemption is not a Tasks-RCU quiescent state.\n\nA long batch therefore never reports a quiescent state, and the\nmigrating task (e.g. kcompactd) becomes a Tasks-RCU holdout, stalling the\nTasks-RCU grace period for minutes, which is common at Meta fleet:\n\n  INFO: rcu_tasks detected stalls on tasks:\n  0000000055349ecc: .. nvcsw: 1157401/1157401 holdout: 1 idle_cpu: -1/56 task:kcompactd0      state:R  running task\n  Call Trace:\n   tdp_mmu_zap_leafs\n   tdp_mmu_next_root\n   gfn_to_pfn_cache_invalidate_start\n   kvm_mmu_notifier_invalidate_range_start\n   __mmu_notifier_invalidate_range_start\n   try_to_migrate_one\n   try_to_migrate\n   migrate_pages_batch\n   migrate_pages\n   compact_zone\n   compact_node\n   kcompactd\n   kthread\n\nUse cond_resched_tasks_rcu_qs() so a quiescent state is reported even\nwhen cond_resched() does nothing.\n\nThis has also been discussed at [1]","publishedAt":"2026-09-11T19:46:59.093Z","updatedAt":"2026-10-19T08:52:09.900Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"8c6d63d434ebb85c6cf3dac1e70a171b183c6614","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"4757542649af56d894e25e30f57cd497dffad53f","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"4996a7bc01ef35570664854dac2530c604981039","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"5dc0daff0341c6baba19c38f47d299ac831d7e99","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"66734981b4d3c105223a13c827c9c73be18d91ad","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"efe8f86c0916f0f74eea74ae21a3b37f728c6bad","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/migrate.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.18","versionType":"semver"},{"version":"6.1.188","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/migrate.c"]}],"references":["https://git.kernel.org/stable/c/8c6d63d434ebb85c6cf3dac1e70a171b183c6614","https://git.kernel.org/stable/c/4757542649af56d894e25e30f57cd497dffad53f","https://git.kernel.org/stable/c/4996a7bc01ef35570664854dac2530c604981039","https://git.kernel.org/stable/c/5dc0daff0341c6baba19c38f47d299ac831d7e99","https://git.kernel.org/stable/c/66734981b4d3c105223a13c827c9c73be18d91ad","https://git.kernel.org/stable/c/efe8f86c0916f0f74eea74ae21a3b37f728c6bad"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89756.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89756","state":"PUBLISHED","datePublished":"2026-09-11T19:46:59.093Z","dateUpdated":"2026-10-19T08:52:09.900Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.763Z"},"containers":{"cna":{"title":"mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/migrate: report RCU-tasks quiescent states in migrate_pages_batch()\n\nmigrate_pages_batch() unmaps each folio before moving it, and every\nunmap runs the mmu_notifier invalidate callbacks.  On KVM hosts\ntry_to_migrate() ends up in kvm_mmu_notifier_invalidate_range_start() ->\ntdp_mmu_zap_leafs(), which is expensive, so unmapping a large batch keeps\nthe CPU busy for a long time.\n\nThe loop already calls cond_resched(), but on PREEMPTION kernels that is\na no-op, and involuntary preemption is not a Tasks-RCU quiescent state.\n\nA long batch therefore never reports a quiescent state, and the\nmigrating task (e.g. kcompactd) becomes a Tasks-RCU holdout, stalling the\nTasks-RCU grace period for minutes, which is common at Meta fleet:\n\n  INFO: rcu_tasks detected stalls on tasks:\n  0000000055349ecc: .. nvcsw: 1157401/1157401 holdout: 1 idle_cpu: -1/56 task:kcompactd0      state:R  running task\n  Call Trace:\n   tdp_mmu_zap_leafs\n   tdp_mmu_next_root\n   gfn_to_pfn_cache_invalidate_start\n   kvm_mmu_notifier_invalidate_range_start\n   __mmu_notifier_invalidate_range_start\n   try_to_migrate_one\n   try_to_migrate\n   migrate_pages_batch\n   migrate_pages\n   compact_zone\n   compact_node\n   kcompactd\n   kthread\n\nUse cond_resched_tasks_rcu_qs() so a quiescent state is reported even\nwhen cond_resched() does nothing.\n\nThis has also been discussed at [1]"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"8c6d63d434ebb85c6cf3dac1e70a171b183c6614","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"4757542649af56d894e25e30f57cd497dffad53f","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"4996a7bc01ef35570664854dac2530c604981039","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"5dc0daff0341c6baba19c38f47d299ac831d7e99","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"66734981b4d3c105223a13c827c9c73be18d91ad","versionType":"git"},{"version":"8315f42295d2667a7f942f154b73a86fd7cb2227","status":"affected","lessThan":"efe8f86c0916f0f74eea74ae21a3b37f728c6bad","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/migrate.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.18","versionType":"semver"},{"version":"6.1.188","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/migrate.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/8c6d63d434ebb85c6cf3dac1e70a171b183c6614"},{"url":"https://git.kernel.org/stable/c/4757542649af56d894e25e30f57cd497dffad53f"},{"url":"https://git.kernel.org/stable/c/4996a7bc01ef35570664854dac2530c604981039"},{"url":"https://git.kernel.org/stable/c/5dc0daff0341c6baba19c38f47d299ac831d7e99"},{"url":"https://git.kernel.org/stable/c/66734981b4d3c105223a13c827c9c73be18d91ad"},{"url":"https://git.kernel.org/stable/c/efe8f86c0916f0f74eea74ae21a3b37f728c6bad"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:52:09.900Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.1.188"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.6.157"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.12.109"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"6.18.50"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.18","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}