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

[Avi K. <av...@qu...>]

Chris Lalancette wrote:
> 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.
>   

You mean the gcc generates wrong code?  It seems fine here (though 
wonderfully obfuscated).

Can you attach an objdump -Sr svm.o?  Also, what gcc version are you using?

-- 
error compiling committee.c: too many arguments to function