[RFC PATCH 19/22] KVM: x86: Allow host and guest access to IA32_[AM]PERF

Mingwei Zhang
2024-11-21T18:53:51Z

Implement MSR read/write handlers for IA32_APERF and IA32_MPERF to
support both host and guest access:

- Host userspace access via KVM_[GS]ET_MSRS only reads/writes the
snapshot values in vcpu->arch.aperfmperf
- Guest writes update both the hardware MSRs (via set_guest_[am]perf)
and the snapshots
- For host-initiated writes of IA32_MPERF, record the current TSC to
establish a new baseline for background cycle accumulation
- Guest reads don't reach these handlers as they access the MSRs directly

Add both MSRs to msrs_to_save_base[] to ensure they are properly
serialized during vCPU state save/restore operations.

Signed-off-by: Mingwei Zhang <mizhang@google.com>
Co-developed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
---
arch/x86/kvm/x86.c | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cd1f1ae86f83f..4394ecb291401 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -334,6 +334,7 @@ static const u32 msrs_to_save_base[] = {
MSR_IA32_UMWAIT_CONTROL,

MSR_IA32_XFD, MSR_IA32_XFD_ERR,
+ MSR_IA32_APERF, MSR_IA32_MPERF,
};

static const u32 msrs_to_save_pmu[] = {
@@ -4151,6 +4152,26 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return 1;
vcpu->arch.msr_misc_features_enables = data;
break;
+ case MSR_IA32_APERF:
+ if ((data || !msr_info->host_initiated) &&
+ !guest_can_use(vcpu, X86_FEATURE_APERFMPERF))
+ return 1;
+
+ vcpu->arch.aperfmperf.guest_aperf = data;
+ if (unlikely(!msr_info->host_initiated))
+ set_guest_aperf(data);
+ break;
+ case MSR_IA32_MPERF:
+ if ((data || !msr_info->host_initiated) &&
+ !guest_can_use(vcpu, X86_FEATURE_APERFMPERF))
+ return 1;
+
+ vcpu->arch.aperfmperf.guest_mperf = data;
+ if (likely(msr_info->host_initiated))
+ vcpu->arch.aperfmperf.host_tsc = rdtsc();
+ else
+ set_guest_mperf(data);
+ break;
#ifdef CONFIG_X86_64
case MSR_IA32_XFD:
if (!msr_info->host_initiated &&
@@ -4524,6 +4545,22 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data = vcpu->arch.guest_fpu.xfd_err;
break;
#endif
+ case MSR_IA32_APERF:
+ /* Guest read access should never reach here. */
+ if (!msr_info->host_initiated)
+ return 1;
+
+ msr_info->data = vcpu->arch.aperfmperf.guest_aperf;
+ break;
+ case MSR_IA32_MPERF:
+ /* Guest read access should never reach here. */
+ if (!msr_info->host_initiated)
+ return 1;
+
+ if (vcpu->arch.mp_state != KVM_MP_STATE_HALTED)
+ kvm_accumulate_background_guest_mperf(vcpu);
+ msr_info->data = vcpu->arch.aperfmperf.guest_mperf;
+ break;
default:
if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
return kvm_pmu_get_msr(vcpu, msr_info);
@@ -7535,6 +7572,11 @@ static void kvm_probe_msr_to_save(u32 msr_index)
if (!(kvm_get_arch_capabilities() & ARCH_CAP_TSX_CTRL_MSR))
return;
break;
+ case MSR_IA32_APERF:
+ case MSR_IA32_MPERF:
+ if (!kvm_cpu_cap_has(KVM_X86_FEATURE_APERFMPERF))
+ return;
+ break;
default:
break;
}
--
2.47.0.371.ga323438b13-goog