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

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Message-ID: <20120530145155.GJ3207@phenom.dumpdata.com>
Date:	Wed, 30 May 2012 10:51:55 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andre Przywara <andre.przywara@....com>, mingo@...e.hu,
	tglx@...utronix.de, jeremy@...p.org, xen-devel@...ts.xensource.com,
	stable@...r.kernel.org#3.4+, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] x86/amd: fix crash as Xen Dom0 on AMD
 Trinity systems

On Wed, May 30, 2012 at 07:50:15AM -0700, H. Peter Anvin wrote:
> On 05/30/2012 07:39 AM, Konrad Rzeszutek Wilk wrote:
> > On Wed, May 30, 2012 at 03:10:02PM +0200, Andre Przywara wrote:
> >> Because we are behind a family check before tweaking the topology
> >> bit, we can use the standard rd/wrmsr variants for the CPUID feature
> >> register.
> >> This fixes a crash when using the kernel as a Xen Dom0 on affected
> >> Trinity systems. The wrmsrl_amd_safe is not properly paravirtualized
> >> yet (this will be fixed in another patch).
> > 
> > So with a rdmsrl_amd_safe and wrmsrl_amd_safe being implemented in
> > the pv_cpu_ops - would this patch even be neccessary?
> > 
> 
> That is still bogus;  a better thing would be to implement the _regs
> interface.  Even better would be to trap and emulate rdmsr/wrmsr!

That is what I meant - implement these two:

	rdmsr_regs = native_rdmsr_safe_regs,
        .wrmsr_regs = native_wrmsr_safe_regs,

Xen already traps the rdmsr/wrms - I believe it just didn't do
anything for this specific MSR.
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