Re: [PATCH v5] KVM: VMX: Execute WBINVD to keep data consistency with assigned devices

Avi Kivity
2010-06-29T12:38:08Z

On 06/29/2010 03:32 PM, Roedel, Joerg wrote:
> On Tue, Jun 29, 2010 at 06:42:57AM -0400, Avi Kivity wrote:
>
>> On 06/29/2010 01:32 PM, Jan Kiszka wrote:
>>
>
>> Correctness is more important than performance. Since we don't know
>> whether the guest needs it or not, we have to enable it. The user may
>> disable it if he likes.
>>
> Can't this code only be enabled if VT-d hardware is detected that does
> not support the snoop force bit? So the user does not have to struggle
> with configuration options that are hard to understand for a
> non-developer.
>
>

It's already this way, that's why we test for
KVM_IOMMU_CACHE_COHERENCY. Jan wants an override for older hardware
which doesn't support a coherent iommu (the wbinvd ipi on task
migrations, on processors that don't support wbinvd exits, is
particularly expensive).

--
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