On Fri, Jan 15, 2021, Xu, Like wrote: > On 2021/1/15 2:55, Sean Christopherson wrote: > > On Mon, Jan 04, 2021, Like Xu wrote: > > > + * Note: KVM disables the co-existence of guest PEBS and host PEBS. > > By "KVM", do you mean KVM's loading of the MSRs provided by > > intel_guest_get_msrs()? > > Because the PMU should really be the entity that controls guest vs. host. > > KVM > > should just be a dumb pipe that handles the mechanics of how values are > > context > > switch. > > The intel_guest_get_msrs() and atomic_switch_perf_msrs() > will work together to disable the co-existence of guest PEBS and host PEBS: > > https://lore.kernel.org/kvm/961e6135-ff6d-86d1-3b7b-a1846ad0e...@intel.com/ > > + > > static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx) > ... > if (nr_msrs > 2 && (msrs[1].guest & msrs[0].guest)) { > msrs[2].guest = pmu->ds_area; > if (nr_msrs > 3) > msrs[3].guest = pmu->pebs_data_cfg; > } > > for (i = 0; i < nr_msrs; i++) > ...
Yeah, that's exactly what I'm complaining about. Splitting the logic for determining the guest values is unnecessarily confusing, and as evidenced by the PEBS_ENABLE bug, potentially fragile. Perf should have full knowledge and control of what values are loaded for the guest. And, the above indexing magic is nigh impossible to follow and _super_ fragile. If we change .guest_get_msrs() to take a struct kvm_pmu pointer, then it can generate the full set of guest values by grabbing ds_area and pebs_data_cfg. Alternatively, .guest_get_msrs() could take the desired guest MSR values directly (ds_area and pebs_data_cfg), but kvm_pmu is vendor agnostic, so I don't see any reason to not just pass the pointer.
