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

["H. Peter Anvin" <hpa@zytor.com>]

On 02/12/2013 04:16 PM, Borislav Petkov wrote:
>
> This family check is redundant, we're already in a 0x10 if-branch
> above. Boris had sent a second version which doesn't have that check:
> http://marc.info/?l=linux-kernel&m=135949774114910 but I don't know how this
> other version has gotten in.
>
> @hpa: maybe replace - patch is still at the top of tip:x86/cpu?
>

I'll check with Ingo if that is doable.

>> +			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?

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.