Re: [Xen-devel] [PATCH] x86/amd: fix crash as Xen Dom0 on AMD Trinity systems

["H. Peter Anvin" <hpa@zytor.com>]

On 05/30/2012 11:17 AM, Borislav Petkov wrote:
> On Wed, May 30, 2012 at 11:00:23AM -0700, H. Peter Anvin wrote:
>> OK.  But there is still the general problem, no?
> 
> With this patch xen crashes go away because they paravirt
> native_{read,write}_msr_safe.
> 
> The other place where we use the amd_safe variants is an obscure K8,
> revC and earlier fix for _some_ BIOSen and this hasn't bitten us yet
> so I'm assuming people haven't run xen on such boxes yet. Does it need
> fixing? Probably, if we really really have to.
> 
> Now, someone probably needs to paravirt the *safe_regs variants in case
> something else decides to use them. I don't know what to do here, do I
> want more paravirt code in there? No. I guess if this is done carefully
> and cleanly, then it should be ok but it can't be done like that - it
> needs to adhere to the current pv_cpu_ops thing which is already there.
> 

I thought I was being told that Xen would trap and emulate the
rdmsr/wrmsr instructions.  I guess they don't want to do that for the
handful of performance-sensitive MSRs there are, but those don't use the
*_regs variants.

	-hpa