Re: [Xen-devel] [PATCH] VT-d: correct a comment and remove useless if() statement

[Chao Gao <chao.gao@xxxxxxxxx>]

On Wed, Apr 12, 2017 at 02:57:23AM -0600, Jan Beulich wrote:
>>>> On 12.04.17 at 02:04, <chao.gao@xxxxxxxxx> wrote:
>> --- a/xen/drivers/passthrough/vtd/intremap.c
>> +++ b/xen/drivers/passthrough/vtd/intremap.c
>> @@ -200,8 +200,9 @@ static void update_irte(struct iommu *iommu, struct 
>> iremap_entry *entry,
>>      else
>>      {
>>          /*
>> -         * If the caller requests an atomic update but we can't meet it, 
>> -         * a bug will be raised.
>> +         * VT-d hardware doesn't update IRTEs behind us, nor the software.
>
>Hmm, so far I was under the impression that in posted mode the
>IRTE could be updated by hardware. Is that not the case? As to

No. I have confirmed this with VT-d architect that VT-d hardware 
doesn't update IRTEs. For posted format, VT-d hardware will atomically
update Posted Interrupt Descriptor, an address recorded in posted
format IRTE.

>software not updating, with there not being any synchronization
>clearly visible around here, I'm afraid this also needs expanding
>on (in the commit message at least, not necessarily in the
>comment).

Will do.

>
>> +         * If a caller want an atomic update from the views of VT-d
>
>wants
>
>Also what do you mean by "from the views of VT-d"?

OK. will fix this too. Do you mean it is (and should be) atomic from software's 
view
, so these words are redundant.

Thanks
Chao

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