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

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

On 03/27/2013 09:45 AM, Stefan Bader wrote:
> 
> Rebooting with smep=1 as a hv argument does not fix it. But I
> would be careful since I just quickly did this without checking
> whether Xen 4.2.1 undestands the flag already.
> 
> Second using x86info --all on bare metal does show bits set for 
> cpuid[7] and /proc/cpuinfo values are consistent across BP and
> APs. So I am a tool for using the wrong tool there.
> 
> So I would say the main issue to look at is why reading cr4 as a 
> HVM guest produces the flags on boot. Surely the hypervisor itself 
> has set certain things up but likely there are some epxectations 
> about the initial setup on boot.
> 

What does x86info and /proc/cpuinfo show in HVM?

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.

        -hpa

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