On Thu, Apr 01, 2021, Paolo Bonzini wrote:
> On 01/04/21 16:38, Maxim Levitsky wrote:
> > +static int kvm_do_deliver_pending_exception(struct kvm_vcpu *vcpu)
> > +{
> > + int class1, class2, ret;
> > +
> > + /* try to deliver current pending exception as VM exit */
> > + if (is_guest_mode(vcpu)) {
> > + ret = kvm_x86_ops.nested_ops->deliver_exception_as_vmexit(vcpu);
> > + if (ret || !vcpu->arch.pending_exception.valid)
> > + return ret;
> > + }
> > +
> > + /* No injected exception, so just deliver the payload and inject it */
> > + if (!vcpu->arch.injected_exception.valid) {
> > + trace_kvm_inj_exception(vcpu->arch.pending_exception.nr,
> > + vcpu->arch.pending_exception.has_error_code,
> > + vcpu->arch.pending_exception.error_code);
> > +queue:
>
> If you move the queue label to the top of the function, you can "goto queue" for #DF as well and you don't need to call kvm_do_deliver_pending_exception again. In fact you can merge this function and kvm_deliver_pending_exception completely:
>
>
> static int kvm_deliver_pending_exception_as_vmexit(struct kvm_vcpu *vcpu)
> {
> WARN_ON(!vcpu->arch.pending_exception.valid);
> if (is_guest_mode(vcpu))
> return kvm_x86_ops.nested_ops->deliver_exception_as_vmexit(vcpu);
> else
> return 0;
> }
>
> static int kvm_merge_injected_exception(struct kvm_vcpu *vcpu)
> {
> /*
> * First check if the pending exception takes precedence
> * over the injected one, which will be reported in the
> * vmexit info.
> */
> ret = kvm_deliver_pending_exception_as_vmexit(vcpu);
> if (ret || !vcpu->arch.pending_exception.valid)
> return ret;
>
> if (vcpu->arch.injected_exception.nr == DF_VECTOR) {
> ...
> return 0;
> }
> ...
> if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY)
> || (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
> ...
> }
> vcpu->arch.injected_exception.valid = false;
> }
>
> static int kvm_deliver_pending_exception(struct kvm_vcpu *vcpu)
> {
> if (!vcpu->arch.pending_exception.valid)
> return 0;
>
> if (vcpu->arch.injected_exception.valid)
> kvm_merge_injected_exception(vcpu);
>
> ret = kvm_deliver_pending_exception_as_vmexit(vcpu));
> if (ret || !vcpu->arch.pending_exception.valid)
I really don't like querying arch.pending_exception.valid to see if the exception
was morphed to a VM-Exit. I also find kvm_deliver_pending_exception_as_vmexit()
to be misleading; to me, that reads as being a command, i.e. "deliver this
pending exception as a VM-Exit".
It' also be nice to make the helpers closer to pure functions, i.e. pass the
exception as a param instead of pulling it from vcpu->arch.
Now that we have static_call, the number of calls into vendor code isn't a huge
issue. Moving nested_run_pending to arch code would help, too. What about
doing something like:
static bool kvm_l1_wants_exception_vmexit(struct kvm_vcpu *vcpu, u8 vector)
{
return is_guest_mode(vcpu) && kvm_x86_l1_wants_exception(vcpu, vector);
}
...
if (!kvm_x86_exception_allowed(vcpu))
return -EBUSY;
if (kvm_l1_wants_exception_vmexit(vcpu, vcpu->arch...))
return kvm_x86_deliver_exception_as_vmexit(...);
> return ret;
>
> trace_kvm_inj_exception(vcpu->arch.pending_exception.nr,
> vcpu->arch.pending_exception.has_error_code,
> vcpu->arch.pending_exception.error_code);
> ...
> }
>
