Re: [Xen-devel] [PATCH v2] VTD/Intremap: Disable Intremap on Chipset 5500/5520/X58 due to errata

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.03.13 at 22:55, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> wrote:
>>  
>> >> And - do you really need to iterate over all buses on segment 0?
>> >> The X58 data sheet says at the top of section 17.1: "All devices
>> >> on the IOH reside on bus 0". I wonder whether you wouldn't
>> >> instead need to do this over all segments, on each bus 0.
>> >
>> > The chipsets do not support multi-segment systems, and we have a
>> > multi-socket affected systems with multiple of these chipsets, with none
>> > of the IOH's on bus 0.
>> 
>> That's contrary to the spec then, and will need clarification.
>> Don, Xiantao?
> 
> For x58,  it is true because it is a UP platform, but it is not true for 
> 5500/5520, it depends on how many IOHs are in the platforms, and also depends 
> on how it is configured by platform, so the spec may only say x58's IOH 
> resides in bus0, but not for applicable for all. 

In which case (considering that neither the most recent [and only]
data sheet rev nor the spec update say so) the question is whether
there's any restriction which buses to look at, or whether the loop
really needs to go over all buses on all segments (the latter of
which is a problem on its own, as Xen may not be able to access the
config space of devices on segments other than 0, as the approval
to use MMCFG may need to come from Dom0). For Andrew's
statement above regarding these chipsets not supporting multi-
segment setups I haven't found confirmation anywhere, and
(considering the potential of extra gluing hardware) may be hard
to be had.

Jan


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