[kvm-devel] [PATCH]: Fix MSR_K7_EVNTSEL{0,3} for SVM

[Chris L. <cla...@re...>]

Avi, Joerg,
     While trying to boot a RHEL-4 guest on latest KVM tip on an AMD machine, I
found that the guest would consistently crash when trying to setup the NMI
watchdog.  I traced it down to the following commit:

51ef1ac7b23ee32bfcc61c229d634fdc1c68b38a

It seems that in that commit, the K7_EVNTSEL MSR's were set to fail if the data
!= 0.  That test is actually fine, the problem is how the code around it is
generated.  That is, we are only supposed to go to unhandled if data != 0; but
for some reason, we are *always* going to unhandled, even when the data == 0.
That causes RHEL-4 kernel to crash.  If I rearrange the code to look like this:

	case MSR_K7_EVNTSEL0:
	case MSR_K7_EVNTSEL1:
	case MSR_K7_EVNTSEL2:
	case MSR_K7_EVNTSEL3:

		if (data != 0)
			return kvm_set_msr_common(vcpu, ecx, data);
		
	default:
		return kvm_set_msr_common(vcpu, ecx, data);
	}

Then everything works again.  A patch that does just this is attached.  It might
be slightly nicer to say "if (data == 0) return 0" and then just fall through to
the default case, but I don't much care either way.

Signed-off-by: Chris Lalancette <cla...@re...>