On Thu, Jun 4, 2020 at 9:20 AM Paolo Bonzini <[email protected]> wrote: > > On 04/06/20 17:16, Sean Christopherson wrote: > > On Thu, Jun 04, 2020 at 09:37:59AM +0800, Xu, Like wrote: > >> On 2020/6/4 4:33, Sean Christopherson wrote: > >>> Unconditionally return true when querying the validity of > >>> MSR_IA32_PERF_CAPABILITIES so as to defer the validity check to > >>> intel_pmu_{get,set}_msr(), which can properly give the MSR a pass when > >>> the access is initiated from host userspace. > >> Regardless of the MSR is emulated or not, is it a really good > >> assumption that > >> the guest cpuids are not properly ready when we do initialization from host > >> userspace > >> ? > > > > I don't know if I would call it a "good assumption" so much as a "necessary > > assumption". KVM_{GET,SET}_MSRS are allowed, and must function correctly, > > if they're called prior to KVM_SET_CPUID{2}. > > Generally speaking this is not the case for the PMU; get_gp_pmc for > example depends on pmu->nr_arch_gp_counters which is initialized based > on CPUID leaf 0xA. > > The assumption that this patch fixes is that you can blindly take the > output of KVM_GET_MSR_INDEX_LIST and pass it to KVM_{GET,SET}_MSRS.
Is that an assumption or an invariant?
