On Wed, Nov 09, 2022, Like Xu wrote: > On 28/10/2022 6:47 am, Sean Christopherson wrote: > > What happens if userspace sets X86_FEATURE_PERFCTR_CORE when its not supported? > > E.g. will KVM be coerced into taking a #GP on a non-existent counter? > > I'm getting a bit tired of this generic issue, what does KVM need to do when > the KVM user space sets a capability that KVM doesn't support (like cpuid). > Should it change the guest cpuid audibly or silently ? Should it report an > error when the guest uses this unsupported capability at run time, or should > it just let the KVM report an error when user space setting the cpuid ? KVM should do nothing unless the bogus CPUID can be used to trigger unexpected and/or unwanted behavior in the kernel, which is why I asked if KVM might end up taking a #GP.
