[RFC PATCH 11/22] KVM: x86: Initialize guest [am]perf at vcpu power-on

Mingwei Zhang
2024-11-21T18:53:37Z

From: Jim Mattson <jmattson@google.com>

The guest's IA32_APERF and IA32_MPERF MSRs start at zero. However,
IA32_MPERF should be incremented whenever the vCPU is in C0, just as
the host's IA32_MPERF MSR is incremented by hardware.

Record the host TSC at vcpu_reset() to start tracking time spent in C0.
Later patches will add the host TSC delta to the guest's stored IA32_MPERF
value at appropriate points.

Signed-off-by: Jim Mattson <jmattson@google.com>
---
arch/x86/include/asm/kvm_host.h | 9 +++++++++
arch/x86/kvm/x86.c | 7 +++++++
2 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 04ef56d10cbb1..067e6ec7f7e9c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -738,6 +738,13 @@ struct kvm_queued_exception {
bool has_payload;
};

+struct kvm_vcpu_aperfmperf {
+ u64 guest_aperf;
+ u64 guest_mperf;
+ u64 host_tsc;
+ bool loaded_while_running;
+};
+
struct kvm_vcpu_arch {
/*
* rip and regs accesses must go through
@@ -1040,6 +1047,8 @@ struct kvm_vcpu_arch {
#if IS_ENABLED(CONFIG_HYPERV)
hpa_t hv_root_tdp;
#endif
+
+ struct kvm_vcpu_aperfmperf aperfmperf;
};

struct kvm_lpage_info {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3c6b0ca91e5f5..d66cccff13347 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12476,6 +12476,13 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)

__kvm_set_xcr(vcpu, 0, XFEATURE_MASK_FP);
__kvm_set_msr(vcpu, MSR_IA32_XSS, 0, true);
+
+ /*
+ * IA32_MPERF should start running now. Record the host TSC
+ * so that we can add the host TSC delta the next time that
+ * we load the guest [am]perf values into the hardware MSRs.
+ */
+ vcpu->arch.aperfmperf.host_tsc = rdtsc();
}

/* All GPRs except RDX (handled below) are zeroed on RESET/INIT. */
--
2.47.0.371.ga323438b13-goog