Allow ktr(4) tracing of all guest exceptions via the tunable

"hw.vmm.trace_guest_exceptions".  To enable this feature set the tunable
to "1" before loading vmm.ko.

Tracing the guest exceptions can be useful when debugging guest triple faults.

Note that there is a performance impact when exception tracing is enabled
since every exception will now trigger a VM-exit.

Also, handle machine check exceptions that happen during guest execution
by vectoring to the host's machine check handler via "int $18".

Discussed with:	grehan
MFC after:	2 weeks

1 files changed, 12 insertions, 0 deletions

diff --git a/sys/amd64/vmm/vmm.c b/sys/amd64/vmm/vmm.c
index e7fbada39fc2..d9cb6f3c1254 100644
--- a/sys/amd64/vmm/vmm.c
+++ b/sys/amd64/vmm/vmm.c
@@ -207,6 +207,11 @@ static int vmm_ipinum;
 SYSCTL_INT(_hw_vmm, OID_AUTO, ipinum, CTLFLAG_RD, &vmm_ipinum, 0,
     "IPI vector used for vcpu notifications");
 
+static int trace_guest_exceptions;
+SYSCTL_INT(_hw_vmm, OID_AUTO, trace_guest_exceptions, CTLFLAG_RDTUN,
+    &trace_guest_exceptions, 0,
+    "Trap into hypervisor on all guest exceptions and reflect them back");
+
 static void
 vcpu_cleanup(struct vm *vm, int i, bool destroy)
 {
@@ -250,6 +255,13 @@ vcpu_init(struct vm *vm, int vcpu_id, bool create)
 	vmm_stat_init(vcpu->stats);
 }
 
+int
+vcpu_trace_exceptions(struct vm *vm, int vcpuid)
+{
+
+	return (trace_guest_exceptions);
+}
+
 struct vm_exit *
 vm_exitinfo(struct vm *vm, int cpuid)
 {