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

Jan Beulich wrote on 2014-05-23:
>>>> 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.

Yes, we definitely need to test it on both machines. From all your previous 
discussions, the cause is that XSA-59 touches AER register without consider 
whether it is owned by firmware. But if hardware doesn't support 
firmware-first, then it has no problem.

Best regards,

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