From: Sean Christopherson seanjc@google.com
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@intel.com Cc: stable@vger.kernel.org Cc: Andrew Cooper Andrew.Cooper3@citrix.com Cc: Peter Zijlstra peterz@infradead.org Cc: Kan Liang kan.liang@linux.intel.com Cc: Andi Kleen ak@linux.intel.com Link: https://lore.kernel.org/all/20220818181530.2355034-1-kan.liang@linux.intel.c... Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20230208204230.1360502-2-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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;