Re: [RFC PATCH 23/41] KVM: x86/pmu: Implement the save/restore of PMU state for Intel CPU

[Sean Christopherson]

On Fri, Jan 26, 2024, Xiong Zhang wrote:
>  static void intel_save_pmu_context(struct kvm_vcpu *vcpu)
>  {
> +	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> +	struct kvm_pmc *pmc;
> +	u32 i;
> +
> +	if (pmu->version != 2) {
> +		pr_warn("only PerfMon v2 is supported for passthrough PMU");
> +		return;
> +	}
> +
> +	/* Global ctrl register is already saved at VM-exit. */
> +	rdmsrl(MSR_CORE_PERF_GLOBAL_STATUS, pmu->global_status);
> +	/* Clear hardware MSR_CORE_PERF_GLOBAL_STATUS MSR, if non-zero. */
> +	if (pmu->global_status)
> +		wrmsrl(MSR_CORE_PERF_GLOBAL_OVF_CTRL, pmu->global_status);
> +
> +	for (i = 0; i < pmu->nr_arch_gp_counters; i++) {
> +		pmc = &pmu->gp_counters[i];
> +		rdpmcl(i, pmc->counter);
> +		rdmsrl(i + MSR_ARCH_PERFMON_EVENTSEL0, pmc->eventsel);
> +		/*
> +		 * Clear hardware PERFMON_EVENTSELx and its counter to avoid
> +		 * leakage and also avoid this guest GP counter get accidentally
> +		 * enabled during host running when host enable global ctrl.
> +		 */
> +		if (pmc->eventsel)
> +			wrmsrl(MSR_ARCH_PERFMON_EVENTSEL0 + i, 0);
> +		if (pmc->counter)
> +			wrmsrl(MSR_IA32_PMC0 + i, 0);
> +	}
> +
> +	rdmsrl(MSR_CORE_PERF_FIXED_CTR_CTRL, pmu->fixed_ctr_ctrl);
> +	/*
> +	 * Clear hardware FIXED_CTR_CTRL MSR to avoid information leakage and
> +	 * also avoid these guest fixed counters get accidentially enabled
> +	 * during host running when host enable global ctrl.
> +	 */
> +	if (pmu->fixed_ctr_ctrl)
> +		wrmsrl(MSR_CORE_PERF_FIXED_CTR_CTRL, 0);
> +	for (i = 0; i < pmu->nr_arch_fixed_counters; i++) {
> +		pmc = &pmu->fixed_counters[i];
> +		rdpmcl(INTEL_PMC_FIXED_RDPMC_BASE | i, pmc->counter);
> +		if (pmc->counter)
> +			wrmsrl(MSR_CORE_PERF_FIXED_CTR0 + i, 0);
> +	}

For the next RFC, please make that it includes AMD support.  Mostly because I'm
pretty all of this code can be in common x86.  The fixed counters are ugly,
but pmu->nr_arch_fixed_counters is guaranteed to '0' on AMD, so it's _just_ ugly,
i.e. not functionally problematic.