Re: [PATCH v4 21/38] KVM: x86/pmu/vmx: Save/load guest IA32_PERF_GLOBAL_CTRL with vm_exit/entry_ctrl

From: Mingwei Zhang
Date: Wed Mar 26 2025 - 16:10:15 EST

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In reply to: Chen, Zide: "Re: [PATCH v4 21/38] KVM: x86/pmu/vmx: Save/load guest IA32_PERF_GLOBAL_CTRL with vm_exit/entry_ctrl"
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On Wed, Mar 26, 2025 at 9:51 AM Chen, Zide <zide.chen@xxxxxxxxx> wrote:
>
>
>
> On 3/24/2025 10:31 AM, Mingwei Zhang wrote:
> > From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> >
> > Intel processor (vmx) provides capability to save/load guest
> > IA32_PERF_GLOBAL_CTRL at vm-exit/vm-entry by setting
> > VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL bit in VM-exit-ctrl or
> > VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL bit in VM-entry-ctrl.
> >
> > Mediated vPMU leverages both capabilities to save/load guest
> > IA32_PERF_GLOBAL_CTRL automatically at vm-exit/vm-entry. Note that the
> > former was introduced in SapphireRapids and later Intel CPUs.
> >
> > If VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL is unavailable, mediated PMU will be
> > disabled. Note that mediated PMU can be enabled by falling back to atomic
> > msr save/retore list. However, that would cause extra overhead per
> > VM-enter/exit.
> >
> > Since these VMX capability bits perform automatic saving/restoring of the
> > PMU global ctrl between VMCS and the HW MSR. No synchronization was
> > performed betwen HW MSR and pmu->global_ctrli, the KVM cached value .
> > Therefore, whenever KVM needs to use this variable, it will need to
> > explicitly read the value from MSR to pmu->global_ctrl. This is especially
> > so when guest doesn't own all PMU counters, i.e., when
> > IA32_PERF_GLOBAL_CTRL is interceped by mediated PMU.
> >
> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> > Co-developed-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> > Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> > ---
> > arch/x86/include/asm/kvm_host.h | 4 ++++
> > arch/x86/include/asm/vmx.h | 1 +
> > arch/x86/kvm/pmu.c | 30 ++++++++++++++++++++++++-
> > arch/x86/kvm/vmx/capabilities.h | 5 +++++
> > arch/x86/kvm/vmx/nested.c | 3 ++-
> > arch/x86/kvm/vmx/pmu_intel.c | 39 ++++++++++++++++++++++++++++++++-
> > arch/x86/kvm/vmx/vmx.c | 22 ++++++++++++++++++-
> > arch/x86/kvm/vmx/vmx.h | 3 ++-
> > 8 files changed, 102 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 0b7af5902ff7..4b3bfefc2d05 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -553,6 +553,10 @@ struct kvm_pmu {
> > unsigned available_event_types;
> > u64 fixed_ctr_ctrl;
> > u64 fixed_ctr_ctrl_rsvd;
> > + /*
> > + * kvm_pmu_sync_global_ctrl_from_vmcs() must be called to update
> > + * this SW-maintained global_ctrl for mediated vPMU before accessing it.
> > + */
> > u64 global_ctrl;
> > u64 global_status;
> > u64 counter_bitmask[2];
> > diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> > index f7fd4369b821..48e137560f17 100644
> > --- a/arch/x86/include/asm/vmx.h
> > +++ b/arch/x86/include/asm/vmx.h
> > @@ -106,6 +106,7 @@
> > #define VM_EXIT_CLEAR_BNDCFGS 0x00800000
> > #define VM_EXIT_PT_CONCEAL_PIP 0x01000000
> > #define VM_EXIT_CLEAR_IA32_RTIT_CTL 0x02000000
> > +#define VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL 0x40000000
> >
> > #define VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR 0x00036dff
> >
> > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> > index 6ad71752be4b..4e8cefcce7ab 100644
> > --- a/arch/x86/kvm/pmu.c
> > +++ b/arch/x86/kvm/pmu.c
> > @@ -646,6 +646,30 @@ void kvm_pmu_deliver_pmi(struct kvm_vcpu *vcpu)
> > }
> > }
> >
> > +static void kvm_pmu_sync_global_ctrl_from_vmcs(struct kvm_vcpu *vcpu)
> > +{
> > + struct msr_data msr_info = { .index = MSR_CORE_PERF_GLOBAL_CTRL };
> > +
> > + if (!kvm_mediated_pmu_enabled(vcpu))
> > + return;
> > +
> > + /* Sync pmu->global_ctrl from GUEST_IA32_PERF_GLOBAL_CTRL. */
> > + kvm_pmu_call(get_msr)(vcpu, &msr_info);
> > +}
> > +
> > +static void kvm_pmu_sync_global_ctrl_to_vmcs(struct kvm_vcpu *vcpu, u64 global_ctrl)
> > +{
> > + struct msr_data msr_info = {
> > + .index = MSR_CORE_PERF_GLOBAL_CTRL,
> > + .data = global_ctrl };
> > +
> > + if (!kvm_mediated_pmu_enabled(vcpu))
> > + return;
> > +
> > + /* Sync pmu->global_ctrl to GUEST_IA32_PERF_GLOBAL_CTRL. */
> > + kvm_pmu_call(set_msr)(vcpu, &msr_info);
> > +}
> > +
> > bool kvm_pmu_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
> > {
> > switch (msr) {
> > @@ -680,7 +704,6 @@ int kvm_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > msr_info->data = pmu->global_status;
> > break;
> > case MSR_AMD64_PERF_CNTR_GLOBAL_CTL:
> > - case MSR_CORE_PERF_GLOBAL_CTRL:
> > msr_info->data = pmu->global_ctrl;
> > break;
> > case MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_CLR:
> > @@ -731,6 +754,9 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>
>
> pmu->global_ctrl doesn't always have the up-to-date guest value, need to
> sync from vmcs/vmbc before comparing it against 'data'.
>
> + kvm_pmu_sync_global_ctrl_from_vmcs(vcpu);
> if (pmu->global_ctrl != data) {

Good catch. Thanks!

This is why I really prefer just unconditionally syncing the global
ctrl from VMCS to pmu->global_ctrl and vice versa.

We might get into similar problems as well in the future.

>
> > diff = pmu->global_ctrl ^ data;
> > pmu->global_ctrl = data;
> > reprogram_counters(pmu, diff);
> > +
> > + /* Propagate guest global_ctrl to GUEST_IA32_PERF_GLOBAL_CTRL. */
> > + kvm_pmu_sync_global_ctrl_to_vmcs(vcpu, data);
> > }
> > break;
> > case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> > @@ -907,6 +933,8 @@ void kvm_pmu_trigger_event(struct kvm_vcpu *vcpu, u64 eventsel)
> >
> > BUILD_BUG_ON(sizeof(pmu->global_ctrl) * BITS_PER_BYTE != X86_PMC_IDX_MAX);
> >
> > + kvm_pmu_sync_global_ctrl_from_vmcs(vcpu);
> > +
> > if (!kvm_pmu_has_perf_global_ctrl(pmu))
> > bitmap_copy(bitmap, pmu->all_valid_pmc_idx, X86_PMC_IDX_MAX);
> > else if (!bitmap_and(bitmap, pmu->all_valid_pmc_idx,
> > diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> > index 013536fde10b..cc63bd4ab87c 100644
> > --- a/arch/x86/kvm/vmx/capabilities.h
> > +++ b/arch/x86/kvm/vmx/capabilities.h
> > @@ -101,6 +101,11 @@ static inline bool cpu_has_load_perf_global_ctrl(void)
> > return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
> > }
> >
> > +static inline bool cpu_has_save_perf_global_ctrl(void)
> > +{
> > + return vmcs_config.vmexit_ctrl & VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL;
> > +}
> > +
> > static inline bool cpu_has_vmx_mpx(void)
> > {
> > return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS;
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index 8a7af02d466e..ecf72394684d 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -7004,7 +7004,8 @@ static void nested_vmx_setup_exit_ctls(struct vmcs_config *vmcs_conf,
> > VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
> > VM_EXIT_LOAD_IA32_EFER | VM_EXIT_SAVE_IA32_EFER |
> > VM_EXIT_SAVE_VMX_PREEMPTION_TIMER | VM_EXIT_ACK_INTR_ON_EXIT |
> > - VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL;
> > + VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL |
> > + VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL;
> >
> > /* We support free control of debug control saving. */
> > msrs->exit_ctls_low &= ~VM_EXIT_SAVE_DEBUG_CONTROLS;
> > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> > index 2a5f79206b02..04a893e56135 100644
> > --- a/arch/x86/kvm/vmx/pmu_intel.c
> > +++ b/arch/x86/kvm/vmx/pmu_intel.c
> > @@ -294,6 +294,11 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > u32 msr = msr_info->index;
> >
> > switch (msr) {
> > + case MSR_CORE_PERF_GLOBAL_CTRL:
> > + if (kvm_mediated_pmu_enabled(vcpu))
> > + pmu->global_ctrl = vmcs_read64(GUEST_IA32_PERF_GLOBAL_CTRL);
> > + msr_info->data = pmu->global_ctrl;
> > + break;
> > case MSR_CORE_PERF_FIXED_CTR_CTRL:
> > msr_info->data = pmu->fixed_ctr_ctrl;
> > break;
> > @@ -339,6 +344,11 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > u64 reserved_bits, diff;
> >
> > switch (msr) {
> > + case MSR_CORE_PERF_GLOBAL_CTRL:
> > + if (kvm_mediated_pmu_enabled(vcpu))
> > + vmcs_write64(GUEST_IA32_PERF_GLOBAL_CTRL,
> > + pmu->global_ctrl);
> > + break;
> > case MSR_CORE_PERF_FIXED_CTR_CTRL:
> > if (data & pmu->fixed_ctr_ctrl_rsvd)
> > return 1;
> > @@ -558,10 +568,37 @@ static void __intel_pmu_refresh(struct kvm_vcpu *vcpu)
> >
> > static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
> > {
> > + struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> > + struct vcpu_vmx *vmx = to_vmx(vcpu);
> > + bool mediated;
> > +
> > __intel_pmu_refresh(vcpu);
> >
> > - exec_controls_changebit(to_vmx(vcpu), CPU_BASED_RDPMC_EXITING,
> > + exec_controls_changebit(vmx, CPU_BASED_RDPMC_EXITING,
> > !kvm_rdpmc_in_guest(vcpu));
> > +
> > + mediated = kvm_mediated_pmu_enabled(vcpu);
> > + if (cpu_has_load_perf_global_ctrl()) {
> > + vm_entry_controls_changebit(vmx,
> > + VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL, mediated);
> > + /*
> > + * Initialize guest PERF_GLOBAL_CTRL to reset value as SDM rules.
> > + *
> > + * Note: GUEST_IA32_PERF_GLOBAL_CTRL must be initialized to
> > + * "BIT_ULL(pmu->nr_arch_gp_counters) - 1" instead of pmu->global_ctrl
> > + * since pmu->global_ctrl is only be initialized when guest
> > + * pmu->version > 1. Otherwise if pmu->version is 1, pmu->global_ctrl
> > + * is 0 and guest counters are never really enabled.
> > + */
> > + if (mediated)
> > + vmcs_write64(GUEST_IA32_PERF_GLOBAL_CTRL,
> > + BIT_ULL(pmu->nr_arch_gp_counters) - 1);
> > + }
> > +
> > + if (cpu_has_save_perf_global_ctrl())
> > + vm_exit_controls_changebit(vmx,
> > + VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL |
> > + VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL, mediated);
> > }
> >
> > static void intel_pmu_init(struct kvm_vcpu *vcpu)
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index ff66f17d6358..38ecf3c116bd 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -4390,6 +4390,13 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
> >
> > if (cpu_has_load_ia32_efer())
> > vmcs_write64(HOST_IA32_EFER, kvm_host.efer);
> > +
> > + /*
> > + * Initialize host PERF_GLOBAL_CTRL to 0 to disable all counters
> > + * immediately once VM exits. Mediated vPMU then call perf_guest_exit()
> > + * to re-enable host perf events.
> > + */
> > + vmcs_write64(HOST_IA32_PERF_GLOBAL_CTRL, 0);
> > }
> >
> > void set_cr4_guest_host_mask(struct vcpu_vmx *vmx)
> > @@ -4457,7 +4464,8 @@ static u32 vmx_get_initial_vmexit_ctrl(void)
> > VM_EXIT_CLEAR_IA32_RTIT_CTL);
> > /* Loading of EFER and PERF_GLOBAL_CTRL are toggled dynamically */
> > return vmexit_ctrl &
> > - ~(VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL | VM_EXIT_LOAD_IA32_EFER);
> > + ~(VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL | VM_EXIT_LOAD_IA32_EFER |
> > + VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL);
> > }
> >
> > void vmx_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
> > @@ -7196,6 +7204,9 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
> > struct perf_guest_switch_msr *msrs;
> > struct kvm_pmu *pmu = vcpu_to_pmu(&vmx->vcpu);
> >
> > + if (kvm_mediated_pmu_enabled(&vmx->vcpu))
> > + return;
> > +
> > pmu->host_cross_mapped_mask = 0;
> > if (pmu->pebs_enable & pmu->global_ctrl)
> > intel_pmu_cross_mapped_check(pmu);
> > @@ -8451,6 +8462,15 @@ __init int vmx_hardware_setup(void)
> > enable_sgx = false;
> > #endif
> >
> > + /*
> > + * All CPUs that support a mediated PMU are expected to support loading
> > + * and saving PERF_GLOBAL_CTRL via dedicated VMCS fields.
> > + */
> > + if (enable_mediated_pmu &&
> > + (WARN_ON_ONCE(!cpu_has_load_perf_global_ctrl() ||
> > + !cpu_has_save_perf_global_ctrl())))
> > + enable_mediated_pmu = false;
> > +
> > /*
> > * set_apic_access_page_addr() is used to reload apic access
> > * page upon invalidation. No need to do anything if not
> > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> > index 5c505af553c8..b282165f98a6 100644
> > --- a/arch/x86/kvm/vmx/vmx.h
> > +++ b/arch/x86/kvm/vmx/vmx.h
> > @@ -510,7 +510,8 @@ static inline u8 vmx_get_rvi(void)
> > VM_EXIT_LOAD_IA32_EFER | \
> > VM_EXIT_CLEAR_BNDCFGS | \
> > VM_EXIT_PT_CONCEAL_PIP | \
> > - VM_EXIT_CLEAR_IA32_RTIT_CTL)
> > + VM_EXIT_CLEAR_IA32_RTIT_CTL | \
> > + VM_EXIT_SAVE_IA32_PERF_GLOBAL_CTRL)
> >
> > #define KVM_REQUIRED_VMX_PIN_BASED_VM_EXEC_CONTROL \
> > (PIN_BASED_EXT_INTR_MASK | \
>

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In reply to: Chen, Zide: "Re: [PATCH v4 21/38] KVM: x86/pmu/vmx: Save/load guest IA32_PERF_GLOBAL_CTRL with vm_exit/entry_ctrl"
Next in thread: Mingwei Zhang: "[PATCH v4 22/38] KVM: x86/pmu: Optimize intel/amd_pmu_refresh() helpers"
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