From 9fb150b264534f2de506844098502bd428b4e1ad Mon Sep 17 00:00:00 2001 From: Greg Kroah-Hartman Date: Thu, 30 Jul 2026 16:13:20 +0200 Subject: [PATCH] 7.1-stable patches added patches: kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch --- ...o-avoid-asid-collision-after-hotplug.patch | 89 +++++++++++++++++++ queue-7.1/series | 1 + 2 files changed, 90 insertions(+) create mode 100644 queue-7.1/kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch diff --git a/queue-7.1/kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch b/queue-7.1/kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch new file mode 100644 index 0000000000..c99a6058ed --- /dev/null +++ b/queue-7.1/kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch @@ -0,0 +1,89 @@ +From 25f744ffa0c8e799e06250ce2e618367b166b0d4 Mon Sep 17 00:00:00 2001 +From: Nikunj A Dadhania +Date: Wed, 15 Jul 2026 06:35:06 +0000 +Subject: KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug +MIME-Version: 1.0 +Content-Type: text/plain; charset=UTF-8 +Content-Transfer-Encoding: 8bit + +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 +@@ -566,7 +566,12 @@ static int svm_enable_virtualization_cpu + return r; + + 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; diff --git a/queue-7.1/series b/queue-7.1/series index dd06cc4950..77dd8210d9 100644 --- a/queue-7.1/series +++ b/queue-7.1/series @@ -741,3 +741,4 @@ sched_ext-move-shared-helpers-from-ext.c-into-internal.h-and-cid.h.patch sched_ext-preserve-rq-tracking-across-local-dsq-dispatch.patch selftests-drv-net-cope-with-slow-env-in-so_txtime.py-test.patch selftests-drv-net-so_txtime-relax-variance-bounds.patch +kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch -- 2.47.3