KVM: x86: Polish exception injection via KVM_SET_GUEST_DEBUG

Decouple KVM_GUESTDBG_INJECT_DB and KVM_GUESTDBG_INJECT_BP from
KVM_GUESTDBG_ENABLE, their are actually orthogonal. At this chance,
avoid triggering the WARN_ON in kvm_queue_exception if there is already
an exception pending and reject such invalid requests.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 14 insertions, 6 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cd6fe0a5797f..ba8958dca3c4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4656,10 +4656,20 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
                                         struct kvm_guest_debug *dbg)
 {
         unsigned long rflags;
-        int i;
+        int i, r;
 
         vcpu_load(vcpu);
 
+        if (dbg->control & (KVM_GUESTDBG_INJECT_DB | KVM_GUESTDBG_INJECT_BP)) {
+                r = -EBUSY;
+                if (vcpu->arch.exception.pending)
+                        goto unlock_out;
+                if (dbg->control & KVM_GUESTDBG_INJECT_DB)
+                        kvm_queue_exception(vcpu, DB_VECTOR);
+                else
+                        kvm_queue_exception(vcpu, BP_VECTOR);
+        }
+
         /*
          * Read rflags as long as potentially injected trace flags are still
          * filtered out.
@@ -4695,14 +4705,12 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 
         kvm_x86_ops->set_guest_debug(vcpu, dbg);
 
-        if (vcpu->guest_debug & KVM_GUESTDBG_INJECT_DB)
-                kvm_queue_exception(vcpu, DB_VECTOR);
-        else if (vcpu->guest_debug & KVM_GUESTDBG_INJECT_BP)
-                kvm_queue_exception(vcpu, BP_VECTOR);
+        r = 0;
 
+unlock_out:
         vcpu_put(vcpu);
 
-        return 0;
+        return r;
 }
 
 /*