Re: [PATCH v2 30/54] KVM: x86/pmu: Implement the save/restore of PMU state for Intel CPU

Mi, Dapeng
2024-05-14T08:08:21Z

On 5/6/2024 1:29 PM, Mingwei Zhang wrote:
> Implement the save/restore of PMU state for pasthrough PMU in Intel. In
> passthrough mode, KVM owns exclusively the PMU HW when control flow goes to
> the scope of passthrough PMU. Thus, KVM needs to save the host PMU state
> and gains the full HW PMU ownership. On the contrary, host regains the
> ownership of PMU HW from KVM when control flow leaves the scope of
> passthrough PMU.
>
> Implement PMU context switches for Intel CPUs and opptunistically use
> rdpmcl() instead of rdmsrl() when reading counters since the former has
> lower latency in Intel CPUs.

It looks rdpmcl() optimization is removed from this patch, right? The
description is not identical with code.

>
> Co-developed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> Signed-off-by: Mingwei Zhang <mizhang@google.com>

The commit tags doesn't follow the rules in Linux document, we need to
change it in next version.

https://docs.kernel.org/process/submitting-patches.html#:~:text=Co%2Ddeveloped%2Dby%3A%20states,work%20on%20a%20single%20patch.

> ---
> arch/x86/kvm/pmu.c | 46 ++++++++++++++++++++++++++++++++++++
> arch/x86/kvm/vmx/pmu_intel.c | 41 +++++++++++++++++++++++++++++++-
> 2 files changed, 86 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 782b564bdf96..13197472e31d 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -1068,14 +1068,60 @@ void kvm_pmu_passthrough_pmu_msrs(struct kvm_vcpu *vcpu)
>
> void kvm_pmu_save_pmu_context(struct kvm_vcpu *vcpu)
> {
> + struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> + struct kvm_pmc *pmc;
> + u32 i;
> +
> lockdep_assert_irqs_disabled();
>
> static_call_cond(kvm_x86_pmu_save_pmu_context)(vcpu);
> +
> + /*
> + * Clear hardware selector MSR content and its counter to avoid
> + * leakage and also avoid this guest GP counter get accidentally
> + * enabled during host running when host enable global ctrl.
> + */
> + for (i = 0; i < pmu->nr_arch_gp_counters; i++) {
> + pmc = &pmu->gp_counters[i];
> + rdmsrl(pmc->msr_counter, pmc->counter);

I understood we want to use common code to manipulate PMU MSRs as much as
possible, but I don't think we should sacrifice performance. rdpmcl() has
better performance than rdmsrl(). If AMD CPUs doesn't support rdpmc
instruction, I think we should move this into vendor specific
xxx_save/restore_pmu_context helpers().

> + rdmsrl(pmc->msr_eventsel, pmc->eventsel);
> + if (pmc->counter)
> + wrmsrl(pmc->msr_counter, 0);
> + if (pmc->eventsel)
> + wrmsrl(pmc->msr_eventsel, 0);
> + }
> +
> + for (i = 0; i < pmu->nr_arch_fixed_counters; i++) {
> + pmc = &pmu->fixed_counters[i];
> + rdmsrl(pmc->msr_counter, pmc->counter);
> + if (pmc->counter)
> + wrmsrl(pmc->msr_counter, 0);
> + }
> }
>
> void kvm_pmu_restore_pmu_context(struct kvm_vcpu *vcpu)
> {
> + struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> + struct kvm_pmc *pmc;
> + int i;
> +
> lockdep_assert_irqs_disabled();
>
> static_call_cond(kvm_x86_pmu_restore_pmu_context)(vcpu);
> +
> + /*
> + * No need to zero out unexposed GP/fixed counters/selectors since RDPMC
> + * in this case will be intercepted. Accessing to these counters and
> + * selectors will cause #GP in the guest.
> + */
> + for (i = 0; i < pmu->nr_arch_gp_counters; i++) {
> + pmc = &pmu->gp_counters[i];
> + wrmsrl(pmc->msr_counter, pmc->counter);
> + wrmsrl(pmc->msr_eventsel, pmu->gp_counters[i].eventsel);
> + }
> +
> + for (i = 0; i < pmu->nr_arch_fixed_counters; i++) {
> + pmc = &pmu->fixed_counters[i];
> + wrmsrl(pmc->msr_counter, pmc->counter);
> + }
> }
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 7852ba25a240..a23cf9ca224e 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -572,7 +572,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
> }
>
> for (i = 0; i < pmu->nr_arch_fixed_counters; i++) {
> - pmu->fixed_counters[i].msr_eventsel = MSR_CORE_PERF_FIXED_CTR_CTRL;
> + pmu->fixed_counters[i].msr_eventsel = 0;
Why to initialize msr_eventsel to 0 instead of the real MSR address here?
> pmu->fixed_counters[i].msr_counter = MSR_CORE_PERF_FIXED_CTR0 + i;
> }
> }
> @@ -799,6 +799,43 @@ static void intel_passthrough_pmu_msrs(struct kvm_vcpu *vcpu)
> vmx_set_intercept_for_msr(vcpu, MSR_CORE_PERF_GLOBAL_OVF_CTRL, MSR_TYPE_RW, msr_intercept);
> }
>
> +static void intel_save_guest_pmu_context(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> +
> + /* 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);
> +
> + 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);
> +}
> +
> +static void intel_restore_guest_pmu_context(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> + u64 global_status, toggle;
> +
> + /* Clear host global_ctrl MSR if non-zero. */
> + wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0);
> + rdmsrl(MSR_CORE_PERF_GLOBAL_STATUS, global_status);
> + toggle = pmu->global_status ^ global_status;
> + if (global_status & toggle)
> + wrmsrl(MSR_CORE_PERF_GLOBAL_OVF_CTRL, global_status & toggle);
> + if (pmu->global_status & toggle)
> + wrmsrl(MSR_CORE_PERF_GLOBAL_STATUS_SET, pmu->global_status & toggle);
> +
> + wrmsrl(MSR_CORE_PERF_FIXED_CTR_CTRL, pmu->fixed_ctr_ctrl);
> +}
> +
> struct kvm_pmu_ops intel_pmu_ops __initdata = {
> .rdpmc_ecx_to_pmc = intel_rdpmc_ecx_to_pmc,
> .msr_idx_to_pmc = intel_msr_idx_to_pmc,
> @@ -812,6 +849,8 @@ struct kvm_pmu_ops intel_pmu_ops __initdata = {
> .cleanup = intel_pmu_cleanup,
> .is_rdpmc_passthru_allowed = intel_is_rdpmc_passthru_allowed,
> .passthrough_pmu_msrs = intel_passthrough_pmu_msrs,
> + .save_pmu_context = intel_save_guest_pmu_context,
> + .restore_pmu_context = intel_restore_guest_pmu_context,
> .EVENTSEL_EVENT = ARCH_PERFMON_EVENTSEL_EVENT,
> .MAX_NR_GP_COUNTERS = KVM_INTEL_PMC_MAX_GENERIC,
> .MIN_NR_GP_COUNTERS = 1,