linux-kernel - Re: [tip:x86/cpu] x86, AMD: Enable WC+ memory type on family 10 processors

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Date:	Wed, 13 Feb 2013 10:06:25 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <bp@...en8.de>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, boris.ostrovsky@....com,
	tglx@...utronix.de, hpa@...ux.intel.com,
	linux-tip-commits@...r.kernel.org,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Asias He <asias@...hat.com>
Subject: Re: [tip:x86/cpu] x86, AMD: Enable WC+ memory type on family 10 processors

On Wed, Feb 13, 2013 at 2:21 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>> +                       rdmsrl(MSR_AMD64_BU_CFG2, value);
>>> +                       value &= ~(1ULL << 24);
>>> +                       wrmsrl(MSR_AMD64_BU_CFG2, value);
>>> +               }
>>>         }
>>>
>>>         rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
>>
>>
>> However, the more serious issue is that that same kernel #GPs when
>> booted in kvm. It seems it cannot stomach that specific MSR, see the
>> second "<-- trapping instruction" below and that BU_CFG2 MSR landing in
>> %ecx in the line before that.
>>
>> Oh, and this happens only with the kvm executable (/usr/bin/kvm) in
>> debian testing. If I use qemu from git, it passes over init_amd just
>> fine.
>>
>> Hmmm..
>
> It #GPs on an MSR, which tends to be a bug in the VMM; RDMSR/WRMSR generally
> kick out to the VMM.  There isn't a huge lot of work we can do about that...
>
> I think Qemu defaults to ignoring unknown-to-it MSRs whereas maybe kvmtool
> croaks?  Pekka?

I think we should also be fine. Cyrillos?
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