6.12-stable patches

added patches:
	kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch

diff --git a/queue-6.12/kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch b/queue-6.12/kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch
new file mode 100644 (file)
index 0000000..d212892
--- /dev/null
+++ b/queue-6.12/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 <nikunj@amd.com>
+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 <nikunj@amd.com>
+
+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 <Chandrakanth.Silveru@amd.com>
+Tested-by: Srikanth Aithal <Srikanth.Aithal@amd.com>
+Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
+Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
+Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
+Message-ID: <20260715063506.672432-1-nikunj@amd.com>
+Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ 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
+@@ -626,7 +626,12 @@ static int svm_enable_virtualization_cpu
+               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;

diff --git a/queue-6.12/series b/queue-6.12/series
index f2a1ce34cc60a58ef652b4e5c7c665483bbde69f..6c5f5ed7640a433c87b82eae0a45a1a15c4ebce5 100644 (file)
--- a/queue-6.12/series
+++ b/queue-6.12/series
@@ -599,3 +599,4 @@ bluetooth-hci_conn-fix-not-cleaning-up-broadcaster-broadcast-source.patch
 bluetooth-hci_conn-fix-not-cleaning-up-pa_link-connections.patch
 bluetooth-hci_conn-fix-memory-leak-in-hci_le_big_terminate.patch
 afs-fix-uninit-var-in-afs_alloc_anon_key.patch
+kvm-svm-bump-asid_generation-on-cpu-online-to-avoid-asid-collision-after-hotplug.patch