[PATCH v5 24/44] KVM: x86: Rework KVM_REQ_MSR_FILTER_CHANGED into a generic RECALC_INTERCEPTS

Sean Christopherson
2025-08-06T19:58:13Z

Rework the MSR_FILTER_CHANGED request into a more generic RECALC_INTERCEPTS
request, and expand the responsibilities of vendor code to recalculate all
intercepts that vary based on userspace input, e.g. instruction intercepts
that are tied to guest CPUID.

Providing a generic recalc request will allow the upcoming mediated PMU
support to trigger a recalc when PMU features, e.g. PERF_CAPABILITIES, are
set by userspace, without having to make multiple calls to/from PMU code.
As a bonus, using a request will effectively coalesce recalcs, e.g. will
reduce the number of recalcs for normal usage from 3+ to 1 (vCPU create,
set CPUID, set PERF_CAPABILITIES (Intel only), set filter).

The downside is that MSR filter changes that are done in isolation will do
a small amount of unnecessary work, but that's already a relatively slow
path, and the cost of recalculating instruction intercepts is negligible.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/include/asm/kvm-x86-ops.h | 2 +-
arch/x86/include/asm/kvm_host.h | 4 ++--
arch/x86/kvm/svm/svm.c | 8 ++++----
arch/x86/kvm/vmx/main.c | 14 +++++++-------
arch/x86/kvm/vmx/vmx.c | 9 +++++++--
arch/x86/kvm/vmx/x86_ops.h | 2 +-
arch/x86/kvm/x86.c | 15 +++++++--------
7 files changed, 29 insertions(+), 25 deletions(-)

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index 18a5c3119e1a..7c240e23bd52 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -138,7 +138,7 @@ KVM_X86_OP(check_emulate_instruction)
KVM_X86_OP(apic_init_signal_blocked)
KVM_X86_OP_OPTIONAL(enable_l2_tlb_flush)
KVM_X86_OP_OPTIONAL(migrate_timers)
-KVM_X86_OP(recalc_msr_intercepts)
+KVM_X86_OP(recalc_intercepts)
KVM_X86_OP(complete_emulated_msr)
KVM_X86_OP(vcpu_deliver_sipi_vector)
KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ff0d753e2b07..b891bd92fc83 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -120,7 +120,7 @@
#define KVM_REQ_TLB_FLUSH_GUEST \
KVM_ARCH_REQ_FLAGS(27, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
#define KVM_REQ_APF_READY KVM_ARCH_REQ(28)
-#define KVM_REQ_MSR_FILTER_CHANGED KVM_ARCH_REQ(29)
+#define KVM_REQ_RECALC_INTERCEPTS KVM_ARCH_REQ(29)
#define KVM_REQ_UPDATE_CPU_DIRTY_LOGGING \
KVM_ARCH_REQ_FLAGS(30, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
#define KVM_REQ_MMU_FREE_OBSOLETE_ROOTS \
@@ -1912,7 +1912,7 @@ struct kvm_x86_ops {
int (*enable_l2_tlb_flush)(struct kvm_vcpu *vcpu);

void (*migrate_timers)(struct kvm_vcpu *vcpu);
- void (*recalc_msr_intercepts)(struct kvm_vcpu *vcpu);
+ void (*recalc_intercepts)(struct kvm_vcpu *vcpu);
int (*complete_emulated_msr)(struct kvm_vcpu *vcpu, int err);

void (*vcpu_deliver_sipi_vector)(struct kvm_vcpu *vcpu, u8 vector);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f7e1e665a826..3d9dcc66a407 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1077,7 +1077,7 @@ static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu)
}
}

-static void svm_recalc_intercepts_after_set_cpuid(struct kvm_vcpu *vcpu)
+static void svm_recalc_intercepts(struct kvm_vcpu *vcpu)
{
svm_recalc_instruction_intercepts(vcpu);
svm_recalc_msr_intercepts(vcpu);
@@ -1225,7 +1225,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu)

svm_hv_init_vmcb(vmcb);

- svm_recalc_intercepts_after_set_cpuid(vcpu);
+ svm_recalc_intercepts(vcpu);

vmcb_mark_all_dirty(vmcb);

@@ -4479,7 +4479,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
if (sev_guest(vcpu->kvm))
sev_vcpu_after_set_cpuid(svm);

- svm_recalc_intercepts_after_set_cpuid(vcpu);
+ svm_recalc_intercepts(vcpu);
}

static bool svm_has_wbinvd_exit(void)
@@ -5181,7 +5181,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {

.apic_init_signal_blocked = svm_apic_init_signal_blocked,

- .recalc_msr_intercepts = svm_recalc_msr_intercepts,
+ .recalc_intercepts = svm_recalc_intercepts,
.complete_emulated_msr = svm_complete_emulated_msr,

.vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector,
diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
index dbab1c15b0cd..68dcafd177a8 100644
--- a/arch/x86/kvm/vmx/main.c
+++ b/arch/x86/kvm/vmx/main.c
@@ -188,18 +188,18 @@ static int vt_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return vmx_get_msr(vcpu, msr_info);
}

-static void vt_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
+static void vt_recalc_intercepts(struct kvm_vcpu *vcpu)
{
/*
- * TDX doesn't allow VMM to configure interception of MSR accesses.
- * TDX guest requests MSR accesses by calling TDVMCALL. The MSR
- * filters will be applied when handling the TDVMCALL for RDMSR/WRMSR
- * if the userspace has set any.
+ * TDX doesn't allow VMM to configure interception of instructions or
+ * MSR accesses. TDX guest requests MSR accesses by calling TDVMCALL.
+ * The MSR filters will be applied when handling the TDVMCALL for
+ * RDMSR/WRMSR if the userspace has set any.
*/
if (is_td_vcpu(vcpu))
return;

- vmx_recalc_msr_intercepts(vcpu);
+ vmx_recalc_intercepts(vcpu);
}

static int vt_complete_emulated_msr(struct kvm_vcpu *vcpu, int err)
@@ -995,7 +995,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
.apic_init_signal_blocked = vt_op(apic_init_signal_blocked),
.migrate_timers = vmx_migrate_timers,

- .recalc_msr_intercepts = vt_op(recalc_msr_intercepts),
+ .recalc_intercepts = vt_op(recalc_intercepts),
.complete_emulated_msr = vt_op(complete_emulated_msr),

.vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector,
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 93b87f9e6dfd..2244ca074e9d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4068,7 +4068,7 @@ void pt_update_intercept_for_msr(struct kvm_vcpu *vcpu)
}
}

-void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
+static void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
{
if (!cpu_has_vmx_msr_bitmap())
return;
@@ -4121,6 +4121,11 @@ void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
*/
}

+void vmx_recalc_intercepts(struct kvm_vcpu *vcpu)
+{
+ vmx_recalc_msr_intercepts(vcpu);
+}
+
static int vmx_deliver_nested_posted_interrupt(struct kvm_vcpu *vcpu,
int vector)
{
@@ -7778,7 +7783,7 @@ void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
~FEAT_CTL_SGX_LC_ENABLED;

/* Recalc MSR interception to account for feature changes. */
- vmx_recalc_msr_intercepts(vcpu);
+ vmx_recalc_intercepts(vcpu);

/* Refresh #PF interception to account for MAXPHYADDR changes. */
vmx_update_exception_bitmap(vcpu);
diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
index 2b3424f638db..2c590ff44ced 100644
--- a/arch/x86/kvm/vmx/x86_ops.h
+++ b/arch/x86/kvm/vmx/x86_ops.h
@@ -52,7 +52,7 @@ void vmx_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
int trig_mode, int vector);
void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu);
bool vmx_has_emulated_msr(struct kvm *kvm, u32 index);
-void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu);
+void vmx_recalc_intercepts(struct kvm_vcpu *vcpu);
void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
void vmx_update_exception_bitmap(struct kvm_vcpu *vcpu);
int vmx_get_feature_msr(u32 msr, u64 *data);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2c34dd3f0222..69f5d9deb75f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6742,7 +6742,11 @@ static int kvm_vm_ioctl_set_msr_filter(struct kvm *kvm,

kvm_free_msr_filter(old_filter);

- kvm_make_all_cpus_request(kvm, KVM_REQ_MSR_FILTER_CHANGED);
+ /*
+ * Recalc MSR intercepts as userspace may want to intercept accesses to
+ * MSRs that KVM would otherwise pass through to the guest.
+ */
+ kvm_make_all_cpus_request(kvm, KVM_REQ_RECALC_INTERCEPTS);

return 0;
}
@@ -10765,13 +10769,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
if (kvm_check_request(KVM_REQ_APF_READY, vcpu))
kvm_check_async_pf_completion(vcpu);

- /*
- * Recalc MSR intercepts as userspace may want to intercept
- * accesses to MSRs that KVM would otherwise pass through to
- * the guest.
- */
- if (kvm_check_request(KVM_REQ_MSR_FILTER_CHANGED, vcpu))
- kvm_x86_call(recalc_msr_intercepts)(vcpu);
+ if (kvm_check_request(KVM_REQ_RECALC_INTERCEPTS, vcpu))
+ kvm_x86_call(recalc_intercepts)(vcpu);

if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
kvm_x86_call(update_cpu_dirty_logging)(vcpu);
--
2.50.1.565.gc32cd1483b-goog