Re: [Xen-devel] [PATCH 1/3] xen/vt-d: need barriers to workaround CLFLUSH

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.05.15 at 08:47, <tiejun.chen@xxxxxxxxx> wrote:
> On 2015/5/5 17:24, Jan Beulich wrote:
>> Btw, isn't the !iommus_incoherent check in that function inverted?
>> I.e. why would we _not_ need to flush caches when IOMMUs
>> are not coherent (and why would flushing be needed when they're
>> coherent anyway)?
>>
> 
> I guess you're misunderstanding this
> 
>      if ( !ecap_coherent(iommu->ecap) )
>          iommus_incoherent = 1;
> 
> So here !iommus_incoherent means IOMMU is coherent and then we don't 
> need to flush cache in this case.

Ah, indeed - I overlooked the "in" in the variable name (together with
the thus resulting double negation in the expression). Sorry for the
noise.

Jan


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