On Tue, Dec 22, 2015 at 10:24:13AM +0300, Pavel Fedin wrote:
> > +On the return path into kvm, user space should set handled to
> > +KVM_EXIT_MSR_HANDLED if it successfully handled the MSR access. Otherwise,
> > +handled should be set to KVM_EXIT_MSR_UNHANDLED, which will cause a general
> > +protection fault to be injected into the vcpu. If an error occurs during 
> > the
> > +return into kvm, the vcpu will not be run and another exit will be 
> > generated
> > +with type set to KVM_EXIT_MSR_COMPLETION_FAILED.
> > +
> > +If exit_reason is KVM_EXIT_MSR_AFTER_WRITE, then the vcpu has executed a 
> > wrmsr
> > +instruction which is handled by kvm but which user space may need to be
> > +notified about. index and data are set as described above; the value of 
> > type
> > +depends on the MSR that was written. handled is ignored on reentry into 
> > kvm.
> 1. Is there any real need to distinguish between KVM_EXIT_MSR_WRITE and 
> KVM_EXIT_MSR_AFTER_WRITE ? IMHO from userland's point of view these are the 
> same.

Indeed.  Perhaps the kernel can set .handled to true to let userspace
know it already took care of it, instead of introducing yet another
exit_reason.  The field would need to be marked in/out, then.

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