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 08:39:15 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Borislav Petkov" <bp@...en8.de>
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>
Subject: Re: [Xen-devel] [PATCH] x86/amd: fix crash as Xen Dom0 on AMD
 Trinity systems

>>> 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).

Jan

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