Re: [Xen-devel] [PATCH] IOMMU: don't disable bus mastering on faults for devices used by Xen or Dom0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.12.12 at 07:08, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> wrote:
> If the phantom device support for IOMMU is in upstream,  is this patch still 
> needed ?

Phantom function is unrelated to the behavioral adjustment here.

>  Basically,  I can't figure out why several faults should be allowed 
> before disabling bus mastering.   Did you meet some real issues ?   Thanks!

I observed quite a different driver failure pattern with and without
this adjustment, but in a contrived environment only. From the
customer data for the problem that prompted the phantom function
work, I could also conclude the same (comparing the driver failure
under native Linux with IOMMU turned on and the one under Xen).

But in any case, I am of the opinion that an occasional fault
shouldn't give reason to disable the device altogether - what we're
aiming at is solely to keep Xen and other domains functional (which
doesn't require as drastic an action as was carried out prior to this
adjustment). Also, afaict native Linux doesn't have any such
disabling behavior at all.

Jan

>> -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Friday, November 30, 2012 5:51 PM
>> To: wei.huang2@xxxxxxx; weiwang.dd@xxxxxxxxx; Zhang, Xiantao; Keir
>> Fraser
>> Cc: Dario Faggioli; xen-devel; Tim Deegan
>> Subject: Re: [Xen-devel] [PATCH] IOMMU: don't disable bus mastering on
>> faults for devices used by Xen or Dom0
>> 
>> >>> On 30.11.12 at 10:42, Keir Fraser <keir@xxxxxxx> wrote:
>> > On 05/11/2012 16:53, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>> >
>> >> Under the assumption that in these cases recurring faults aren't a
>> >> security issue and it can be expected that the drivers there are
>> >> going to try to take care of the problem.
>> >>
>> >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> >
>> > This one's sat a while with no comments...
>> 
>> It's in already (26133:fdb69dd527cd), with Tim's and Dario's ack (who were
>> the ones involved in creating the original change this modifies).
>> 
>> But yes, we're having a general response problem for IOMMU related stuff -
>> I already asked for this to be a topic on the next community call.
>> 
>> Jan




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