From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 331DE58FD22 for ; Fri, 11 Sep 2026 20:06:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789157168; cv=none; b=lgwrUWe9z5v3gW5bqV967UVOZd9BHqct0BR5caCwwwxLMgOTPTLbg0UTmu88UA7n+Hc9mGDtcvEWmTkbmJGBxCaURccbTA/HO9j8OOzZ4jMTzh+mBAK1N+uMzK5BtmJiS1/x7SheBpUGrjJy+lZk9H3vu+NZGz8Pk6hhYNeYMWA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789157168; c=relaxed/simple; bh=gry5JorefIWtRUpR0dCnryyAbtQQAqDjR7FT5b7/ymE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=kXRMf1CWWnSknEmf1jSME5l/RhMm+6utOe8CqFt86xP59epJXd0wGU9cbzKbnxBM9jtkgQVX2j37/WvTat4aIiguWzsTyeCaGgrtCgaf80Vc/6SVgszHLW6FWyeFmFCyGLJgcUjPTdmLCQTky/2mQrVILBRaq21SrDNoHQNsbGY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=AUmvaeH3; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="AUmvaeH3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9A9201F000FF; Fri, 11 Sep 2026 20:06:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789157161; bh=v1hfXKnfa0hYII0WKigCd1zeAxPX8JFQ21WrYS1bzps=; h=From:To:Cc:Subject:Date:Reply-To; b=AUmvaeH3Z7IbM99KDtmNe5grUpjuKwthggezUDWL7ik9mYvQQ6wKfarAdPmq4fYbZ FC9t6hNIZz9nYiBzUEjWpL4ADPjJk0bvCWGzPYAv+wZfGXqdUNDyOueyVdW56VvHPN DplvHvJdApkBJ3j3GMuKxcm+6hDMn106CqgiTa0E= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-89756: mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch() Date: Fri, 11 Sep 2026 21:47:25 +0200 Message-ID: <2026091108-CVE-2026-89756-bab7@gregkh> X-Mailer: git-send-email 2.55.0 Reply-To: , Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3208; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=Y1x3DJdcWPbhOLmbDp2hN8HJdnpDelXjm8orPzpFCfM=; b=owGbwMvMwCRo6H6F97bub03G02pJDFlLIieI6uiUbTjtWV21UHL1m4r5HQc3ygUx7CtIE9mVv 8KypTumI5aFQZCJQVZMkeXLNp6j+ysOKXoZ2p6GmcPKBDKEgYtTACZyfjHDgn35N33uXV5ie+bE QffXUTPFhHNFPzPM078370lsWJn4i7qWjJmd56tZvwVuAQA= X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch() migrate_pages_batch() unmaps each folio before moving it, and every unmap runs the mmu_notifier invalidate callbacks. On KVM hosts try_to_migrate() ends up in kvm_mmu_notifier_invalidate_range_start() -> tdp_mmu_zap_leafs(), which is expensive, so unmapping a large batch keeps the CPU busy for a long time. The loop already calls cond_resched(), but on PREEMPTION kernels that is a no-op, and involuntary preemption is not a Tasks-RCU quiescent state. A long batch therefore never reports a quiescent state, and the migrating task (e.g. kcompactd) becomes a Tasks-RCU holdout, stalling the Tasks-RCU grace period for minutes, which is common at Meta fleet: INFO: rcu_tasks detected stalls on tasks: 0000000055349ecc: .. nvcsw: 1157401/1157401 holdout: 1 idle_cpu: -1/56 task:kcompactd0 state:R running task Call Trace: tdp_mmu_zap_leafs tdp_mmu_next_root gfn_to_pfn_cache_invalidate_start kvm_mmu_notifier_invalidate_range_start __mmu_notifier_invalidate_range_start try_to_migrate_one try_to_migrate migrate_pages_batch migrate_pages compact_zone compact_node kcompactd kthread Use cond_resched_tasks_rcu_qs() so a quiescent state is reported even when cond_resched() does nothing. This has also been discussed at [1] The Linux kernel CVE team has assigned CVE-2026-89756 to this issue. Affected and fixed versions =========================== Fixed in 6.12.109 with commit 4996a7bc01ef35570664854dac2530c604981039 Fixed in 6.18.50 with commit 5dc0daff0341c6baba19c38f47d299ac831d7e99 Fixed in 7.2.4 with commit 66734981b4d3c105223a13c827c9c73be18d91ad Fixed in 7.3-rc1 with commit efe8f86c0916f0f74eea74ae21a3b37f728c6bad Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2026-89756 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: mm/migrate.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: 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