Re: [PATCH RFC v2] vPCI: account for hidden devices

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.05.2023 17:02, Roger Pau Monné wrote:
> On Thu, May 25, 2023 at 04:39:51PM +0200, Jan Beulich wrote:
>> On 24.05.2023 17:56, Roger Pau Monné wrote:
>>> On Wed, May 24, 2023 at 03:45:58PM +0200, Jan Beulich wrote:
>>>> --- a/xen/drivers/vpci/header.c
>>>> +++ b/xen/drivers/vpci/header.c
>>>> @@ -218,6 +218,7 @@ static int modify_bars(const struct pci_
>>>>      struct vpci_header *header = &pdev->vpci->header;
>>>>      struct rangeset *mem = rangeset_new(NULL, NULL, 0);
>>>>      struct pci_dev *tmp, *dev = NULL;
>>>> +    const struct domain *d;
>>>>      const struct vpci_msix *msix = pdev->vpci->msix;
>>>>      unsigned int i;
>>>>      int rc;
>>>> @@ -285,9 +286,11 @@ static int modify_bars(const struct pci_
>>>>  
>>>>      /*
>>>>       * Check for overlaps with other BARs. Note that only BARs that are
>>>> -     * currently mapped (enabled) are checked for overlaps.
>>>> +     * currently mapped (enabled) are checked for overlaps. Note also that
>>>> +     * for Dom0 we also need to include hidden, i.e. DomXEN's, devices.
>>>>       */
>>>> -    for_each_pdev ( pdev->domain, tmp )
>>>> +for ( d = pdev->domain; ; d = dom_xen ) {//todo
>>>
>>> Looking at this again, I think this is slightly more complex, as during
>>> runtime dom0 will get here with pdev->domain == hardware_domain OR
>>> dom_xen, and hence you also need to account that devices that have
>>> pdev->domain == dom_xen need to iterate over devices that belong to
>>> the hardware_domain, ie:
>>>
>>> for ( d = pdev->domain; ;
>>>       d = (pdev->domain == dom_xen) ? hardware_domain : dom_xen )
>>
>> Right, something along these lines. To keep loop continuation expression
>> and exit condition simple, I'll probably prefer
>>
>> for ( d = pdev->domain != dom_xen ? pdev->domain : hardware_domain;
>>       ; d = dom_xen )
> 
> LGTM.  I would add parentheses around the pdev->domain != dom_xen
> condition, but that's just my personal taste.
> 
> We might want to add an
> 
> ASSERT(pdev->domain == hardware_domain || pdev->domain == dom_xen);
> 
> here, just to remind that this chunk must be revisited when adding
> domU support (but you can also argue we haven't done this elsewhere),
> I just feel here it's not so obvious we don't want do to this for
> domUs.

I could add such an assertion, if only ...

>>> And we likely want to limit this to devices that belong to the
>>> hardware_domain or to dom_xen (in preparation for vPCI being used for
>>> domUs).
>>
>> I'm afraid I don't understand this remark, though.
> 
> This was looking forward to domU support, so that you already cater
> for pdev->domain not being hardware_domain or dom_xen, but we might
> want to leave that for later, when domU support is actually
> introduced.

... I understood why this checking doesn't apply to DomU-s as well,
in your opinion.

Jan