From: Dave Voutila <dv@sisu.io>
Subject: vmm: classify injected #DB as hardware exception
To: tech@openbsd.org
Cc: Mike Larkin <mlarkin@nested.page>
Date: Wed, 02 Sep 2026 10:18:00 -0400

Both VMX and SVM currently encode an injected #DB as a software
exception.

Using the software-exception type also gives the hardware the wrong
instruction-completion semantics while delivering the event. Move #DB
next to #UD in both injection paths, where it is encoded as a hardware
exception without an error code.

ok?

---
diff e7450dffd6c02a765d93e405c0a5751cf3f2b9f3 c597b118780d9e1062c05ddde4ba76f673c3fede
commit - e7450dffd6c02a765d93e405c0a5751cf3f2b9f3
commit + c597b118780d9e1062c05ddde4ba76f673c3fede
blob - 48b8ac55514e79d373b80601e6ca04f236613c93
blob + 82b2ec36d9d1149814d736fdf6cc9b5bbb3380a5
--- sys/arch/amd64/amd64/vmm_machdep.c
+++ sys/arch/amd64/amd64/vmm_machdep.c
@@ -3879,6 +3879,7 @@ vcpu_run_vmx(struct vcpu *vcpu, struct vm_run_params *
 				/* Software Exceptions */
 				eii |= (4ULL << 8);
 				break;
+			case VMM_EX_DB:
 			case VMM_EX_UD:
 				/* Hardware exception, no error code. */
 				eii |= (3ULL << 8);
@@ -6781,13 +6782,13 @@ vcpu_run_svm(struct vcpu *vcpu, struct vm_run_params *
 			switch (vcpu->vc_inject.vie_vector) {
 			case VMM_EX_BP:
 			case VMM_EX_OF:
-			case VMM_EX_DB:
 				/*
 				 * Software exception.
 				 * XXX check nRIP support.
 				 */
 				vmcb->v_eventinj |= (4ULL << 8);
 				break;
+			case VMM_EX_DB:
 			case VMM_EX_UD:
 				/* Hardware exception, no error code. */
 				vmcb->v_eventinj |= (3ULL << 8);