[PATCH v4 3/7] KVM: SVM: Inject #HV when Restricted Injection is active

Melody Wang
2026-04-24T17:44:00Z

When Restricted Injection is active, only #HV exceptions can be injected into
the SEV-SNP guest. Detect that, and then follow the #HV doorbell communication
from the GHCB specification to inject the interrupt or exception.

Co-developed-by: Thomas Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Melody Wang <huibo.wang@amd.com>
---
arch/x86/kvm/svm/sev.c | 164 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.c | 14 +++-
arch/x86/kvm/svm/svm.h | 21 ++++++
3 files changed, 197 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index f09c4236fb5e..509a4f8b5073 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -5321,3 +5321,167 @@ void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa)

free_page((unsigned long)vmsa);
}
+
+static void prepare_hv_injection(struct vcpu_svm *svm, struct hvdb *hvdb)
+{
+ if (hvdb->events.no_further_signal)
+ return;
+
+ svm->vmcb->control.event_inj = HV_VECTOR |
+ SVM_EVTINJ_TYPE_EXEPT |
+ SVM_EVTINJ_VALID;
+ svm->vmcb->control.event_inj_err = 0;
+
+ hvdb->events.no_further_signal = 1;
+}
+
+static void unmap_hvdb(struct kvm_vcpu *vcpu, struct kvm_host_map *map)
+{
+ kvm_vcpu_unmap(vcpu, map);
+}
+
+static struct hvdb *map_hvdb(struct kvm_vcpu *vcpu, struct kvm_host_map *map)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ if (!VALID_PAGE(svm->sev_es.hvdb_gpa))
+ return NULL;
+
+ if (kvm_vcpu_map(vcpu, gpa_to_gfn(svm->sev_es.hvdb_gpa), map)) {
+ vcpu_unimpl(vcpu, "snp: error mapping #HV doorbell page [%#llx] from guest\n",
+ svm->sev_es.hvdb_gpa);
+
+ return NULL;
+ }
+
+ return map->hva;
+}
+
+static void __sev_snp_inject(enum inject_type type, struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+ struct kvm_host_map hvdb_map;
+ struct hvdb *hvdb;
+
+ hvdb = map_hvdb(vcpu, &hvdb_map);
+ if (!hvdb) {
+ WARN_ONCE(1, "Restricted Injection enabled, hvdb page mapping failed\n");
+ return;
+ }
+
+ hvdb->events.vector = vcpu->arch.interrupt.nr;
+
+ prepare_hv_injection(svm, hvdb);
+
+ unmap_hvdb(vcpu, &hvdb_map);
+}
+
+bool sev_snp_queue_exception(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ if (!sev_snp_is_rinj_active(vcpu))
+ return false;
+
+ /*
+ * Restricted Injection is enabled, only #HV is supported.
+ * If the vector is not HV_VECTOR, do not inject the exception,
+ * then return true to skip the original injection path.
+ */
+ if (WARN_ONCE(vcpu->arch.exception.vector != HV_VECTOR,
+ "Restricted Injection enabled, exception vector %u injection not supported\n",
+ vcpu->arch.exception.vector))
+ return true;
+
+ /*
+ * An intercept likely occurred during #HV delivery, so re-inject it
+ * using the current HVDB pending event values.
+ */
+ svm->vmcb->control.event_inj = HV_VECTOR |
+ SVM_EVTINJ_TYPE_EXEPT |
+ SVM_EVTINJ_VALID;
+ svm->vmcb->control.event_inj_err = 0;
+
+ return true;
+}
+
+bool sev_snp_inject(enum inject_type type, struct kvm_vcpu *vcpu)
+{
+ if (!sev_snp_is_rinj_active(vcpu))
+ return false;
+
+ __sev_snp_inject(type, vcpu);
+
+ return true;
+}
+
+void sev_snp_cancel_injection(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+ struct kvm_host_map hvdb_map;
+ struct hvdb *hvdb;
+
+ if (!sev_snp_is_rinj_active(vcpu))
+ return;
+
+ if (!svm->vmcb->control.event_inj)
+ return;
+
+ if (WARN_ONCE((svm->vmcb->control.event_inj & SVM_EVTINJ_VEC_MASK) != HV_VECTOR,
+ "Restricted Injection enabled, %u vector not supported\n",
+ svm->vmcb->control.event_inj & SVM_EVTINJ_VEC_MASK))
+ return;
+
+ /*
+ * Copy the information in the doorbell page into the event injection
+ * fields to complete the cancellation flow.
+ */
+ hvdb = map_hvdb(vcpu, &hvdb_map);
+ if (!hvdb)
+ return;
+
+ if (!hvdb->events.pending_events) {
+ /* No pending events, then event_inj field should be 0 */
+ WARN_ON_ONCE(svm->vmcb->control.event_inj);
+ goto out;
+ }
+
+ /* Copy info back into event_inj field (replaces #HV) */
+ svm->vmcb->control.event_inj = SVM_EVTINJ_VALID;
+
+ if (hvdb->events.vector)
+ svm->vmcb->control.event_inj |= hvdb->events.vector |
+ SVM_EVTINJ_TYPE_INTR;
+
+ hvdb->events.pending_events = 0;
+
+out:
+ unmap_hvdb(vcpu, &hvdb_map);
+}
+
+/*
+ * sev_snp_blocked() is for each vector - interrupt, NMI and MCE. It is
+ * checking if there is an interrupt handled by the guest when
+ * another interrupt is pending. So hvdb->events.vector will be used for
+ * checking while no_further_signal is signaling to the guest that a #HV
+ * is presented by the hypervisor. So no_further_signal is checked when
+ * a #HV needs to be presented to the guest.
+ */
+bool sev_snp_blocked(enum inject_type type, struct kvm_vcpu *vcpu)
+{
+ struct kvm_host_map hvdb_map;
+ struct hvdb *hvdb;
+ bool blocked;
+
+ /* Indicate interrupts are blocked if doorbell page can't be mapped */
+ hvdb = map_hvdb(vcpu, &hvdb_map);
+ if (!hvdb)
+ return true;
+
+ /* Indicate interrupts blocked based on guest acknowledgment */
+ blocked = !!hvdb->events.vector;
+
+ unmap_hvdb(vcpu, &hvdb_map);
+
+ return blocked;
+}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 826d60527297..739cffe12cd1 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -392,6 +392,9 @@ static void svm_inject_exception(struct kvm_vcpu *vcpu)
svm_update_soft_interrupt_rip(vcpu, ex->vector))
return;

+ if (sev_snp_queue_exception(vcpu))
+ return;
+
svm->vmcb->control.event_inj = ex->vector
| SVM_EVTINJ_VALID
| (ex->has_error_code ? SVM_EVTINJ_VALID_ERR : 0)
@@ -3807,9 +3810,11 @@ static void svm_inject_irq(struct kvm_vcpu *vcpu, bool reinjected)
}

trace_kvm_inj_virq(intr->nr, intr->soft, reinjected);
- ++vcpu->stat.irq_injections;

- svm->vmcb->control.event_inj = intr->nr | SVM_EVTINJ_VALID | type;
+ if (!sev_snp_inject(INJECT_IRQ, vcpu))
+ svm->vmcb->control.event_inj = intr->nr | SVM_EVTINJ_VALID | type;
+
+ ++vcpu->stat.irq_injections;
}

static void svm_fixup_nested_rips(struct kvm_vcpu *vcpu)
@@ -3984,6 +3989,9 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
if (!gif_set(svm))
return true;

+ if (sev_snp_is_rinj_active(vcpu))
+ return sev_snp_blocked(INJECT_IRQ, vcpu);
+
if (is_guest_mode(vcpu)) {
/* As long as interrupts are being delivered... */
if ((svm->nested.ctl.int_ctl & V_INTR_MASKING_MASK)
@@ -4334,6 +4342,8 @@ static void svm_cancel_injection(struct kvm_vcpu *vcpu)
struct vcpu_svm *svm = to_svm(vcpu);
struct vmcb_control_area *control = &svm->vmcb->control;

+ sev_snp_cancel_injection(vcpu);
+
control->exit_int_info = control->event_inj;
control->exit_int_info_err = control->event_inj_err;
control->event_inj = 0;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 4ab58307bf75..b4627884c36f 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -55,6 +55,10 @@ extern int tsc_aux_uret_slot __ro_after_init;

extern struct kvm_x86_ops svm_x86_ops __initdata;

+enum inject_type {
+ INJECT_IRQ,
+};
+
/*
* Clean bits in VMCB.
* VMCB_ALL_CLEAN_MASK might also need to
@@ -968,6 +972,17 @@ void sev_gmem_invalidate(kvm_pfn_t start, kvm_pfn_t end);
int sev_gmem_max_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, bool is_private);
struct vmcb_save_area *sev_decrypt_vmsa(struct kvm_vcpu *vcpu);
void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa);
+bool sev_snp_queue_exception(struct kvm_vcpu *vcpu);
+bool sev_snp_inject(enum inject_type type, struct kvm_vcpu *vcpu);
+void sev_snp_cancel_injection(struct kvm_vcpu *vcpu);
+bool sev_snp_blocked(enum inject_type type, struct kvm_vcpu *vcpu);
+static inline bool sev_snp_is_rinj_active(struct kvm_vcpu *vcpu)
+{
+ struct kvm_sev_info *sev = &to_kvm_svm(vcpu->kvm)->sev_info;
+
+ return is_sev_snp_guest(vcpu) &&
+ (sev->vmsa_features & SVM_SEV_FEAT_RESTRICTED_INJECTION);
+};
#else
static inline struct page *snp_safe_alloc_page_node(int node, gfp_t gfp)
{
@@ -1005,6 +1020,12 @@ static inline struct vmcb_save_area *sev_decrypt_vmsa(struct kvm_vcpu *vcpu)
return NULL;
}
static inline void sev_free_decrypted_vmsa(struct kvm_vcpu *vcpu, struct vmcb_save_area *vmsa) {}
+
+static inline bool sev_snp_queue_exception(struct kvm_vcpu *vcpu) { return false; }
+static inline bool sev_snp_inject(enum inject_type type, struct kvm_vcpu *vcpu) { return false; }
+static inline void sev_snp_cancel_injection(struct kvm_vcpu *vcpu) {}
+static inline bool sev_snp_blocked(enum inject_type type, struct kvm_vcpu *vcpu) { return false; }
+static inline bool sev_snp_is_rinj_active(struct kvm_vcpu *vcpu) { return false; }
#endif

/* vmenter.S */
--
2.43.0