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

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Date:	Thu, 31 May 2012 18:55:23 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	Andre Przywara <andre.przywara@....com>,
	Jacob Shin <jacob.shin@....com>, mingo@...e.hu,
	jeremy@...p.org, tglx@...utronix.de, xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: [Xen-devel] [PATCH] x86/amd: fix crash as Xen Dom0 on AMD
 Trinity systems

On Thu, May 31, 2012 at 08:39:15AM +0100, Jan Beulich wrote:
> >>> On 30.05.12 at 20:17, Borislav Petkov <bp@...en8.de> wrote:
> > On Wed, May 30, 2012 at 11:00:23AM -0700, H. Peter Anvin wrote:
> > 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.
> 
> This again is something that shouldn't even be attempted under
> Xen. The hypervisor, unless really old, does this (and wouldn't
> allow the write by any domain - privileged or not - anyway).
> 
> There's one more user though - the code triggered by the
> "show_msr=" command line option. This one indeed requires
> rdmsr_safe_regs to be functional (albeit under Xen, once
> again, this won't work currently anyway for those MRS on
> old CPUs where the special key in %edi is required, which the
> emulation code in Xen doesn't support).

This doesn't look right. Yinghai, why does generic x86 code use
rdmsrl_amd_safe - it should simply use rdmsrl_safe.

-- 
Regards/Gruss,
Boris.
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