This is a note to let you know that I've just added the patch titled
KVM: x86/pmu: Disable vPMU support on hybrid CPUs (host PMUs)
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-x86-pmu-disable-vpmu-support-on-hybrid-cpus-host-pmus.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4d7404e5ee0066e9a9e8268675de8a273b568b08 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Date: Wed, 8 Feb 2023 20:42:29 +0000
Subject: KVM: x86/pmu: Disable vPMU support on hybrid CPUs (host PMUs)
From: Sean Christopherson <seanjc@xxxxxxxxxx>
commit 4d7404e5ee0066e9a9e8268675de8a273b568b08 upstream.
Disable KVM support for virtualizing PMUs on hosts with hybrid PMUs until
KVM gains a sane way to enumeration the hybrid vPMU to userspace and/or
gains a mechanism to let userspace opt-in to the dangers of exposing a
hybrid vPMU to KVM guests. Virtualizing a hybrid PMU, or at least part of
a hybrid PMU, is possible, but it requires careful, deliberate
configuration from userspace.
E.g. to expose full functionality, vCPUs need to be pinned to pCPUs to
prevent migrating a vCPU between a big core and a little core, userspace
must enumerate a reasonable topology to the guest, and guest CPUID must be
curated per vCPU to enumerate accurate vPMU capabilities.
The last point is especially problematic, as KVM doesn't control which
pCPU it runs on when enumerating KVM's vPMU capabilities to userspace,
i.e. userspace can't rely on KVM_GET_SUPPORTED_CPUID in it's current form.
Alternatively, userspace could enable vPMU support by enumerating the
set of features that are common and coherent across all cores, e.g. by
filtering PMU events and restricting guest capabilities. But again, that
requires userspace to take action far beyond reflecting KVM's supported
feature set into the guest.
For now, simply disable vPMU support on hybrid CPUs to avoid inducing
seemingly random #GPs in guests, and punt support for hybrid CPUs to a
future enabling effort.
Reported-by: Jianfeng Gao <jianfeng.gao@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20220818181530.2355034-1-kan.liang@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20230208204230.1360502-2-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/pmu.h | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -164,15 +164,27 @@ static inline void kvm_init_pmu_capabili
{
bool is_intel = boot_cpu_data.x86_vendor == X86_VENDOR_INTEL;
- perf_get_x86_pmu_capability(&kvm_pmu_cap);
-
- /*
- * For Intel, only support guest architectural pmu
- * on a host with architectural pmu.
- */
- if ((is_intel && !kvm_pmu_cap.version) || !kvm_pmu_cap.num_counters_gp)
+ /*
+ * Hybrid PMUs don't play nice with virtualization without careful
+ * configuration by userspace, and KVM's APIs for reporting supported
+ * vPMU features do not account for hybrid PMUs. Disable vPMU support
+ * for hybrid PMUs until KVM gains a way to let userspace opt-in.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU))
enable_pmu = false;
+ if (enable_pmu) {
+ perf_get_x86_pmu_capability(&kvm_pmu_cap);
+
+ /*
+ * For Intel, only support guest architectural pmu
+ * on a host with architectural pmu.
+ */
+ if ((is_intel && !kvm_pmu_cap.version) ||
+ !kvm_pmu_cap.num_counters_gp)
+ enable_pmu = false;
+ }
+
if (!enable_pmu) {
memset(&kvm_pmu_cap, 0, sizeof(kvm_pmu_cap));
return;
Patches currently in stable-queue which might be from seanjc@xxxxxxxxxx are
queue-6.1/perf-x86-refuse-to-export-capabilities-for-hybrid-pmus.patch
queue-6.1/kvm-x86-pmu-disable-vpmu-support-on-hybrid-cpus-host-pmus.patch
queue-6.1/kvm-initialize-all-of-the-kvm_debugregs-structure-before-sending-it-to-userspace.patch
