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 6F816453A2E; Thu, 30 Jul 2026 16:18:51 +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=1785428332; cv=none; b=gvwYjeEbandn5pekC45iKjJzgREm5w0dwrq7/JwBzVDqrDIFx6lMdDOSspdhE+3BBC5EoQqvgtLMgt8am6Eo8VWvlQzq6pzGF/LNuD4cZ6XGePwfECQRg5cGXHqqxZVLwZL9hyGz7ZF6vtLB9nxJqBo/ep0bh5WOxXrCbqdgP+A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785428332; c=relaxed/simple; bh=to2dJgzfT7LZkDNEbNxqdYGWgzLr2G1nfzGPifUWRqg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=lqQnF6Z2uCdC5DCMHCijWnAg/9W3vjttyotRtBc2IFjvEJzgqWCgjSGgJ922fi80QaRn+K/i+2RYLhRUyeksL1YYO8QyZ+krlash/vp1kFFDEIWd0PJBwf0YskhLb+6F9lXqBAlwt0ewKS0DukqJsA0zY9NR9CqWK0Ui1ii2ZSY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=iWAbHwVq; 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="iWAbHwVq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 815701F000E9; Thu, 30 Jul 2026 16:18:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1785428331; bh=gFzu6JYHr4erCX7InsAFump0XdaoJ+C8XLPv+vzKrLA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=iWAbHwVqZHR9yOHSUcU9hRBExbmHavS8pAn7/I2hu919hc3h2uXSC4Jy+qG02no6Q nDnCsDjYfPhpw5jXm1n9VW/2IgV9T/gDH35JHx3wdNWUNEUxsmFlkMF3i/GOYkg680 CHpSrj4/+F3RhpSir5Rb6t9a4VLRqkWvdvfSMJOc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chandrakanth Silveru , Srikanth Aithal , K Prateek Nayak , Tom Lendacky , Nikunj A Dadhania , Paolo Bonzini Subject: [PATCH 6.6 484/484] KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug Date: Thu, 30 Jul 2026 16:16:21 +0200 Message-ID: <20260730141434.007541864@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260730141423.392222816@linuxfoundation.org> References: <20260730141423.392222816@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nikunj A Dadhania commit 25f744ffa0c8e799e06250ce2e618367b166b0d4 upstream. If a vCPU stays scheduled out (or blocked) while the last pCPU it ran on goes through a hotplug cycle (online->offline->online), and the vCPU then resumes execution on the same pCPU, then it is possible for it to run with an ASID that has now been assigned to a different vCPU, resulting in stale TLB translations being used. svm_enable_virtualization_cpu() resets asid_generation to 1 and sets next_asid to max_asid + 1 on every CPU online event, including hotplug cycles. Because next_asid starts beyond the pool boundary, the first call to new_asid() after an online event always wraps the pool, incrementing asid_generation to 2 and assigning ASIDs starting from min_asid. Consider two vCPUs from different VMs, vCPU-A pinned to CPU-X holding asid_generation=2 and ASID=N from before the hotplug event: 1. CPU-X goes offline and back online: asid_generation resets to 1, next_asid = max_asid + 1. 2. One or more vCPUs migrate to CPU-X and call new_asid(), wrapping the pool and consuming ASIDs starting from min_asid. Eventually vCPU-B from a different VM is assigned asid_generation=2, ASID=N — the same ASID that vCPU-A held before the hotplug. 3. vCPU-A enters pre_svm_run() on CPU-X: current_vmcb->cpu is unchanged so the migration branch is skipped. Its saved asid_generation=2 matches sd->asid_generation=2, so the generation check silently passes and vCPU-A continues running with ASID=N — the same ASID just freshly assigned to vCPU-B. Both vCPUs from different VMs now run on CPU-X with the same ASID, causing them to share NPT TLB entries and producing stale translations. The collision manifests as a KVM internal error (Suberror: 1, emulation failure). The NPT page fault reports a faulting GPA far outside the VM's physical memory range — a sign of stale TLB translations being used. KVM falls back to instruction emulation, which fails on FPU/XSave instructions (XRSTOR, STMXCSR) that the emulator does not implement. Fix this by incrementing asid_generation instead of resetting it to 1 in svm_enable_virtualization_cpu(). On module load, asid_generation starts at 0 (memset) and the increment produces 1, identical to the old behaviour. On subsequent hotplug cycles the generation advances beyond any value a vCPU previously observed on this CPU, so the generation check in pre_svm_run() reliably forces new_asid() on every vCPU after every hotplug cycle. Fixes: 774c47f1d78e ("[PATCH] KVM: cpu hotplug support") Reported-by: Chandrakanth Silveru Tested-by: Srikanth Aithal Reviewed-by: K Prateek Nayak Reviewed-by: Tom Lendacky Signed-off-by: Nikunj A Dadhania Message-ID: <20260715063506.672432-1-nikunj@amd.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/svm/svm.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -637,7 +637,12 @@ static int svm_hardware_enable(void) return -EBUSY; sd = per_cpu_ptr(&svm_data, me); - sd->asid_generation = 1; + /* + * Bump the current asid_generation value to ensure any vCPU that + * previously ran on this CPU sees a stale generation and is forced + * to acquire a new ASID, preventing a latent ASID collision. + */ + sd->asid_generation++; sd->max_asid = cpuid_ebx(SVM_CPUID_FUNC) - 1; sd->next_asid = sd->max_asid + 1; sd->min_asid = max_sev_asid + 1;