Re: [PATCH v2 2/9] KVM: x86: Set guest DR6 by kvm_queue_exception_p() in instruction emulation

[Sean Christopherson]

On Mon, May 11, 2026, Sean Christopherson wrote:
> On Mon, May 11, 2026, Sean Christopherson wrote:
> > On Thu, Dec 18, 2025, Hou Wenlong wrote:
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index ab298bfa7d9f..f33ce947633e 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -8925,7 +8925,9 @@ static void inject_emulated_exception(struct kvm_vcpu *vcpu)
> > >  {
> > >  	struct x86_exception *ex = &vcpu->arch.emulate_ctxt->exception;
> > >  
> > > -	if (ex->vector == PF_VECTOR)
> > > +	if (ex->vector == DB_VECTOR)
> > > +		kvm_queue_exception_e(vcpu, DB_VECTOR, ex->dr6);
> > 
> > This should be kvm_queue_exception_p().  I also think pivoting on DB_VECTOR is
> > the wrong approach. 
> 
> Gah, never mind, didn't look at the next patch.

Actually, that's a good excuse to provide kvm_inject_emulated_db() in this patch,
even though it doesn't become truly necessary until the next patch.  Eliminating
some of the code movement in the next patch will yield a smaller diff, and make
it easier to see that there's change in the !KVM_GUESTDBG_USE_HW_BP case.

@@ -8976,23 +8998,36 @@ static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
        }
 }
 
-static void kvm_inject_emulated_db(struct kvm_vcpu *vcpu, unsigned long dr6)
+static int kvm_inject_emulated_db(struct kvm_vcpu *vcpu, unsigned long dr6)
 {
+       struct kvm_run *kvm_run = vcpu->run;
+
+       if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) {
+               kvm_run->debug.arch.dr6 = dr6 | DR6_ACTIVE_LOW;
+               kvm_run->debug.arch.pc = kvm_get_linear_rip(vcpu);
+               kvm_run->debug.arch.exception = DB_VECTOR;
+               kvm_run->exit_reason = KVM_EXIT_DEBUG;
+               return 0;
+       }
+
        kvm_queue_exception_p(vcpu, DB_VECTOR, dr6);
+       return 1;
 }
 
-static void inject_emulated_exception(struct kvm_vcpu *vcpu)
+static int inject_emulated_exception(struct kvm_vcpu *vcpu)
 {
        struct x86_exception *ex = &vcpu->arch.emulate_ctxt->exception;
 
        if (ex->vector == DB_VECTOR)
-               kvm_inject_emulated_db(vcpu, ex->dr6);
-       else if (ex->vector == PF_VECTOR)
+               return kvm_inject_emulated_db(vcpu, ex->dr6);
+
+       if (ex->vector == PF_VECTOR)
                kvm_inject_emulated_page_fault(vcpu, ex);
        else if (ex->error_code_valid)
                kvm_queue_exception_e(vcpu, ex->vector, ex->error_code);
        else
                kvm_queue_exception(vcpu, ex->vector);
+       return 1;
 }
 
 static struct x86_emulate_ctxt *alloc_emulate_ctxt(struct kvm_vcpu *vcpu)