Hi Akihiko, On Thu, 30 Jul 2026 at 07:36, Akihiko Odaki <[email protected]> wrote: ... > > Sashiko flagged that this can leave the perf event out of sync with > > the sysreg, which looks plausible: on a pCPU with no registered pPMU > > this returns without recreating the event, so a guest event-type > > change there updates the sysreg but not the event, and after migrating > > back to a pCPU the original pPMU covers, kvm_pmc_enable_perf_event() > > re-enables the stale event instead of recreating it. > > > > I know you treat the no-pPMU case as out of spec, but the dropped > > update lands once the vCPU is back on a normal pCPU. Is this intended? > > "[PATCH v9 06/16] KVM: arm64: PMU: Recreate events after MDCR_EL2 > changes" calls kvm_pmu_stop_counter() in kvm_vcpu_reload_pmu(), so it > does not matter whether this function calls kvm_pmu_stop_counter(). > > The other changes that require recreating the event are currently not > handled at all as Sashiko complains [1]. I'll fix that as done in > MDCR_EL2 setters in the next version. > > That said, I do not intend to add any extra complexity to provide any > guarantee for a system with unsupported PMU variation except that the > user can notice and react to that (i.e., the taint is reported and no > oops happens due to NULL dereference). The patch message is somewhat > misleading in this aspect so I'm going to fix that in the next version.
I see, yes, fixing the changelog would help. Thanks, /fuad > > [1] > https://sashiko.dev/#/patchset/[email protected]?part=6 > > Regards, > Akihiko Odaki
