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

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

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On 2015-05-24 17:28, Jan Kiszka wrote:
> 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.

Just rebased by kvm patch queue for some new entries - in this old one
is still there. What can we do about it?

Jan



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