[PATCH v4 4/7] KVM: SVM: Inject NMIs when Restricted Injection is active

Melody Wang
2026-04-24T17:44:25Z

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 NMIs.

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 | 19 ++++++++++++++++---
arch/x86/kvm/svm/svm.c | 8 ++++++++
arch/x86/kvm/svm/svm.h | 1 +
3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 509a4f8b5073..61e1e54deb07 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -5369,7 +5369,10 @@ static void __sev_snp_inject(enum inject_type type, struct kvm_vcpu *vcpu)
return;
}

- hvdb->events.vector = vcpu->arch.interrupt.nr;
+ if (type == INJECT_NMI)
+ hvdb->events.nmi = 1;
+ else
+ hvdb->events.vector = vcpu->arch.interrupt.nr;

prepare_hv_injection(svm, hvdb);

@@ -5449,10 +5452,17 @@ void sev_snp_cancel_injection(struct kvm_vcpu *vcpu)
/* Copy info back into event_inj field (replaces #HV) */
svm->vmcb->control.event_inj = SVM_EVTINJ_VALID;

+ /*
+ * KVM only injects a single event each time (prepare_hv_injection),
+ * so when events.nmi is true, the vector will be zero
+ */
if (hvdb->events.vector)
svm->vmcb->control.event_inj |= hvdb->events.vector |
SVM_EVTINJ_TYPE_INTR;

+ if (hvdb->events.nmi)
+ svm->vmcb->control.event_inj |= SVM_EVTINJ_TYPE_NMI;
+
hvdb->events.pending_events = 0;

out:
@@ -5478,8 +5488,11 @@ bool sev_snp_blocked(enum inject_type type, struct kvm_vcpu *vcpu)
if (!hvdb)
return true;

- /* Indicate interrupts blocked based on guest acknowledgment */
- blocked = !!hvdb->events.vector;
+ /* Indicate NMIs and interrupts blocked based on guest acknowledgment */
+ if (type == INJECT_NMI)
+ blocked = hvdb->events.nmi;
+ else
+ blocked = !!hvdb->events.vector;

unmap_hvdb(vcpu, &hvdb_map);

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 739cffe12cd1..925e284374b6 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3727,6 +3727,9 @@ static void svm_inject_nmi(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);

+ if (sev_snp_inject(INJECT_NMI, vcpu))
+ goto status;
+
svm->vmcb->control.event_inj = SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_NMI;

if (svm->nmi_l1_to_l2)
@@ -3741,6 +3744,8 @@ static void svm_inject_nmi(struct kvm_vcpu *vcpu)
svm->nmi_masked = true;
svm_set_iret_intercept(svm);
}
+
+status:
++vcpu->stat.nmi_injections;
}

@@ -3957,6 +3962,9 @@ bool svm_nmi_blocked(struct kvm_vcpu *vcpu)
if (!gif_set(svm))
return true;

+ if (sev_snp_is_rinj_active(vcpu))
+ return sev_snp_blocked(INJECT_NMI, vcpu);
+
if (is_guest_mode(vcpu) && nested_exit_on_nmi(svm))
return false;

diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index b4627884c36f..16cb76b9fdd5 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -57,6 +57,7 @@ extern struct kvm_x86_ops svm_x86_ops __initdata;

enum inject_type {
INJECT_IRQ,
+ INJECT_NMI,
};

/*
--
2.43.0