Re: [Xen-devel] [PATCH RFC] VT-d: honor firmware-first mode in XSA-59 workaround code

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.05.14 at 03:03, <yang.z.zhang@xxxxxxxxx> wrote:
> Andrew Cooper wrote on 2014-05-22:
>> On 22/05/14 11:33, Jan Beulich wrote:
>>>>>> On 22.05.14 at 12:19, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> No.  We have not observed an issue from XSA-59.
>>>> 
>>>> The version of XenServer we had the issue with didn't contain any
>>>> of the
>>>> XSA-59 fixes at the point that the problem was observed.
>>> Then what was yesterday's alert about then? I.e. do we have any
>>> indication that the workaround as is may cause problems, and that
>>> hence the (relatively involved) patch here is needed at all? And,
>>> how are you intending to test this patch if you haven't even seen an
>>> issue?
>> 
>> As part of finding the root cause of our issue, we identified that
>> just as Dom0 must not play with AER in firmware first mode, Xen must not 
> play either.
> 
> I saw upstream Linux has the patch to handle this case in 2009.

Yes, yet all patches so far went through without anyone (me
included) pointing this out during review.

>> I believe that we have XSA-59 affected hardware with both
>> firmware-first and non-firmware-first HEST tables, so we should be
> 
> why non-firmware-first hardware also affected? It seems only firmware-first 
> hardware is buggy.

"Buggy" is perhaps the wrong term here; "problematic" would seem a
better fit. And I think you misread Andrew's reply - we certainly need
to test the patch on both HEST-with-FF and HEST-without-FF systems,
even if only the former would suffer from the presumed regression.

Jan


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