Re: [Xen-devel] [PATCH 4/4] iommu: add rmrr Xen command line option for extra rmrrs

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.06.15 at 02:39, <kevin.tian@xxxxxxxxx> wrote:
>>  From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Monday, June 01, 2015 5:17 PM
>> >>> On 01.06.15 at 08:30, <kevin.tian@xxxxxxxxx> wrote:
>> >>  From: elena.ufimtseva@xxxxxxxxxx 
>> >> --- a/docs/misc/xen-command-line.markdown
>> >> +++ b/docs/misc/xen-command-line.markdown
>> >> @@ -1185,6 +1185,19 @@ Specify the host reboot method.
>> >>  'efi' instructs Xen to reboot using the EFI reboot call (in EFI mode by
>> >>   default it will use that method first).
>> >>
>> >> +### rmrr
>> >> +> '=
>> start<-end>=[s1]bdf1[,[s1]bdf2[,...]];start<-end>=[s2]bdf1[,[s2]bdf2[,...]]
>> >> +
>> >> +Define RMRRs units that are missing from ACPI table along with device
>> >> +they belong to and use them for 1:1 mapping. End addresses can be
>> omitted
>> >> +and one page will be mapped. The ranges are inclusive when start and
>> end
>> >> +are specified.If segement of the first device is not specified, segment 
>> >> zero
>> >> will be used.
>> >> +If other segments are not specified, first device segment will be used.
>> >> +If segments are specified for every device and not equal, an error will 
>> >> be
>> >> reported.
>> >
>> > Since you only allow devices under same segment for a given rmrr range,
>> > would it be simpler to enforce that explicitly in the format? e.g.:
>> >
>> > = start<-end>=[s1]bdf1[,bdf2[,...]];
>> 
>> While that might simplify the code, I think it's better to allow the
>> user to specify canonical device coordinates, which would include
>> a segment number. Plus ...
>> 
>> > Then you don't need to verify whether segment in later bdfs is specified 
>> > and
>> > different from 1st bdf.
>> 
>> ... verification could not be dropped, unless we altered parse_pci()
>> to have a way to not accept a segment number at all.
>> 
> 
> Is that already the case? otherwise below comment and earlier patch 3/4 is
> meaningless:
> 
> + If other segments are not specified, first device segment will be used.

That function currently allows (but doesn't require) the segment
part to be missing. Other than what we would need here it implies
segment 0 if not specified.

Jan


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