Re: [Xen-devel] Xen HVM regression on certain Intel CPUs

["H. Peter Anvin" <hpa@xxxxxxxxx>]

On 03/27/2013 10:17 AM, Stefan Bader wrote:
>> What does x86info and /proc/cpuinfo show in HVM?
> 
> x86info cpuid[7].ebx = 0xbbb and /proc/cpuinfo also shows smep
> set.

On all CPUs?

>> The inbound %cr4 shouldn't matter at all, we try to not rely on
>> it.
>> 
>> If the hypervisor presents SMEP to the guest then the guest is
>> pretty obviously going to try to use it.
> 
> To me it looks like when bootstrapping the APs things are not yet
> ready to use it. If I did not miss something, the only place that
> the saved contents of cr4 are used is in startup_32 when the cpus
> are brought up. And then just stop dead. Would need to read more
> code but a bit weird why the BP is not affected.

This feels like a bug in Xen, but I don't know for sure yet.  Either
which way, it is odd.  That write to cr4 should be entirely legitimate.

        -hpa



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