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

Commit Message

Mingwei Zhang Nov. 21, 2024, 6:53 p.m. UTC

From: Jim Mattson <[e-mail]>

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 <[e-mail]>
---
 arch/x86/include/asm/kvm_host.h | 9 +++++++++
 arch/x86/kvm/x86.c              | 7 +++++++
 2 files changed, 16 insertions(+)

Patch

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. */