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

From: Mingwei Zhang
Date: Mon Mar 24 2025 - 13:43:18 EST

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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)
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 | \
--
2.49.0.395.g12beb8f557-goog

Next message: Arnd Bergmann: "[PATCH 06/10] zlib: add module description"
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In reply to: Mingwei Zhang: "[PATCH v4 20/38] KVM: x86/pmu: Check if mediated vPMU can intercept rdpmc"
Next in thread: 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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