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

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Message-ID: <4FC664E1.9050504@zytor.com>
Date:	Wed, 30 May 2012 11:20:17 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jacob Shin <jacob.shin@....com>,
	Andre Przywara <andre.przywara@....com>, jeremy@...p.org,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	Jan Beulich <JBeulich@...e.com>, mingo@...e.hu,
	tglx@...utronix.de
Subject: Re: [Xen-devel] [PATCH] x86/amd: fix crash as Xen Dom0 on AMD Trinity
 systems

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

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