Re: [Xen-devel] [PATCH v7] VT-d: use correct BDF for VF to search VT-d unit

[Chao Gao <chao.gao@xxxxxxxxx>]

On Wed, Aug 23, 2017 at 08:31:51AM +0100, Roger Pau Monné wrote:
>On Wed, Aug 23, 2017 at 01:20:13AM -0600, Jan Beulich wrote:
>> >>> On 23.08.17 at 09:16, <roger.pau@xxxxxxxxxx> wrote:
>> > On Wed, Aug 23, 2017 at 09:05:14AM +0800, Chao Gao wrote:
>> >> On Tue, Aug 22, 2017 at 06:43:49AM -0600, Jan Beulich wrote:
>> >> >>>> On 21.08.17 at 23:52, <chao.gao@xxxxxxxxx> wrote:
>> >> >> --- a/xen/include/xen/pci.h
>> >> >> +++ b/xen/include/xen/pci.h
>> >> >> @@ -39,6 +39,10 @@
>> >> >>  #define PCI_SBDF3(s,b,df) ((((s) & 0xffff) << 16) | PCI_BDF2(b, df))
>> >> >>  
>> >> >>  struct pci_dev_info {
>> >> >> +    /*
>> >> >> +     * When 'is_virtfn' is set, 'is_extfn' is re-used to indicate 
>> >> >> whether
>> >> >> +     * the PF of this VF is an extended function.
>> >> >> +     */
>> >> >
>> >> >I'd be inclined to extend the comment by appending ", as a VF itself
>> >> >can never be an extended function." Is that correct? If so, would
>> >> 
>> >> Hi, Jan and Roger.
>> >> 
>> >> Strictly speaking, the VF can be an extended function. The definition is
>> >> within ARI device (in this kind of device, device field is treated as an
>> >> extension of function number) and function number is greater than 7. But
>> >> this field isn't used as we don't care about whether a VF is or not an
>> >> extended function (at least at present).
>> >> 
>> >> Eric reviewed this patch and told me we may match
>> >> 'if ( pdev->info.is_extfn )' in acpi_find_matched_drhd_unit.
>> >> So we may introduce a new field like what I do in v6 or check
>> >> 'pdev->info.is_virtfn' first in acpi_find_matched_drhd_unit (maybe other
>> >> places we check pdev->info.is_extfn).
>> >> 
>> >> Which one do you prefer?
>> > 
>> > Looking at this again I'm not sure why you need any modifications to
>> > acpi_find_matched_drhd_unit. If the virtual function is an extended
>> > function pdev->bus should be equal to pdev->info.physfn.bus, in which
>> > case the already existing is_extfn check will already DTRT?
>> > 
>> > Ie: an extended VF should always have the same bus as the PF it
>> > belongs to, unless I'm missing something.
>> 
>> Why would that be?
>
>It is my understanding (which might be wrong), that an extended
>function simply uses 8 bits for the function number, which on a
>traditional device would be used for both the slot and the function
>number.
>
>So extended functions have no slot, but the bus number is the same for
>all of them, or else they would belong to different devices due to the
>difference in the bus numbers.
>
>Maybe what I'm missing is whether it is possible to have a device with
>virtual functions that expand across several buses?

It is not true. Please refer to the 2.1.2 VF Discovery of SR-IOV spec.
The numbers of VF can be larger than 256 and so it is definite that
sometimes VF's bus number would be different from the PF's.

Thanks
Chao

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