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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/04/17 09:57, 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?

No.  The IRTE is just a translation structure, so conceptually similar
to a pagetable.

With posted interrupts, it is the PI block in memory (referenced by the
IRTE) which gets written to by hardware.

~Andrew

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