[PATCH v2 2/5] KVM: nVMX: Handle pending #DB when injecting INIT VM-exit

Oliver Upton
2020-01-28T09:27:35Z

SDM 27.3.4 states that the 'pending debug exceptions' VMCS field will
be populated if a VM-exit caused by an INIT signal takes priority over a
debug-trap. Emulate this behavior when synthesizing an INIT signal
VM-exit into L1.

Fixes: 558b8d50dbff ("KVM: x86: Fix INIT signal handling in various CPU states")
Signed-off-by: Oliver Upton <oupton@google.com>
---
arch/x86/kvm/vmx/nested.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 95b3f4306ac2..aba16599ca69 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3572,6 +3572,27 @@ static void nested_vmx_inject_exception_vmexit(struct kvm_vcpu *vcpu,
nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI, intr_info, exit_qual);
}

+static inline bool nested_vmx_check_pending_dbg(struct kvm_vcpu *vcpu)
+{
+ return vcpu->arch.exception.nr == DB_VECTOR &&
+ vcpu->arch.exception.pending &&
+ vcpu->arch.exception.has_payload;
+}
+
+/*
+ * If a higher priority VM-exit is delivered before a debug-trap, hardware will
+ * set the 'pending debug exceptions' field appropriately for reinjection on the
+ * next VM-entry.
+ */
+static void nested_vmx_set_pending_dbg(struct kvm_vcpu *vcpu)
+{
+ vmcs_writel(GUEST_PENDING_DBG_EXCEPTIONS, vcpu->arch.exception.payload);
+ vcpu->arch.exception.has_payload = false;
+ vcpu->arch.exception.payload = 0;
+ vcpu->arch.exception.pending = false;
+ vcpu->arch.exception.injected = true;
+}
+
static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -3584,6 +3605,8 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
test_bit(KVM_APIC_INIT, &apic->pending_events)) {
if (block_nested_events)
return -EBUSY;
+ if (nested_vmx_check_pending_dbg(vcpu))
+ nested_vmx_set_pending_dbg(vcpu);
clear_bit(KVM_APIC_INIT, &apic->pending_events);
nested_vmx_vmexit(vcpu, EXIT_REASON_INIT_SIGNAL, 0, 0);
return 0;
--
2.25.0.341.g760bfbb309-goog