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

From: Pekka Enberg
Date: Wed Feb 13 2013 - 03:06:49 EST

On Wed, Feb 13, 2013 at 2:21 AM, H. Peter Anvin <hpa@xxxxxxxxx> 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?
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at