Re: [PATCH v2] KVM: SVM: Sync g_pat with guest-written PAT value

[Jan Kiszka <jan.kiszka@web.de>]

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On 2015-04-21 14:21, Radim Krčmář wrote:
> 2015-04-21 13:09+0200, Paolo Bonzini:
>>
>>
>> On 20/04/2015 19:25, Jan Kiszka wrote:
>>> When hardware supports the g_pat VMCB field, we can use it for emulating
>>> the PAT configuration that the guest configures by writing to the
>>> corresponding MSR.
>>>
>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> I'm not sure about this.  The problem is that, unlike Intel, AMD has no
>> way for the host to force its PAT value and ignore the guest's.  I'm
>> worried about potential performance problems in the guest.
> 
> We already set g_pat to 0x0007040600070406ULL in init_vmcb().
> This patch uses caching that the guest expects, which might improve
> performance as well.  I think it's a step in right direction even if we
> somehow optimize cache coherent cases later.

This topic is still open - and the patch still applies.

Jan


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