On Thu, Apr 11, 2024 at 10:21 AM Liang, Kan <kan.liang@xxxxxxxxxxxxxxx> wrote: > > > > On 2024-04-11 1:04 p.m., Sean Christopherson wrote: > > On Fri, Jan 26, 2024, Xiong Zhang wrote: > >> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx> > >> > >> Define and apply the PERF_PMU_CAP_VPMU_PASSTHROUGH flag for the version 4 > >> and later PMUs > > > > Why? I get that is an RFC, but it's not at all obvious to me why this needs to > > take a dependency on v4+. > > The IA32_PERF_GLOBAL_STATUS_RESET/SET MSRs are introduced in v4. They > are used in the save/restore of PMU state. Please see PATCH 23/41. > So it's limited to v4+ for now. Prior to version 4, semi-passthrough is possible, but IA32_PERF_GLOBAL_STATUS has to be intercepted and emulated, since it is non-trivial to set bits in this MSR.
