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



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