Re: [PATCH v6 2/3] xen/arm: Enable the existing x86 virtual PCI support for ARM.

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.10.2021 12:33, Bertrand Marquis wrote:
>> On 15 Oct 2021, at 11:24, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 15.10.2021 11:52, Bertrand Marquis wrote:
>>>> On 15 Oct 2021, at 09:32, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
>>>> On Thu, Oct 14, 2021 at 03:49:50PM +0100, Bertrand Marquis wrote:
>>>>> @@ -752,6 +752,19 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
>>>>>
>>>>>    check_pdev(pdev);
>>>>>
>>>>> +#ifdef CONFIG_ARM
>>>>> +    /*
>>>>> +     * On ARM PCI devices discovery will be done by Dom0. Add vpci 
>>>>> handler when
>>>>> +     * Dom0 inform XEN to add the PCI devices in XEN.
>>>>> +     */
>>>>> +    ret = vpci_add_handlers(pdev);
>>>>> +    if ( ret )
>>>>> +    {
>>>>> +        printk(XENLOG_ERR "Setup of vPCI failed: %d\n", ret);
>>>>> +        goto out;
>>>>> +    }
>>>>> +#endif
>>>>
>>>> I think vpci_add_handlers should be called after checking that
>>>> pdev->domain is != NULL, so I would move this chunk a bit below.
>>>
>>> On arm this would prevent the dom0less use case or to have the PCI
>>> bus enumerated from an other domain.
>>> @oleksandr: can you comment on this one, you might have a better
>>> answer than me on this ?
>>
>> Well, without Xen doing the enumeration, some other entity would need
>> to do so, including the reporting to Xen. Obviously without a Dom0 it
>> would be ambiguous which domain to assign the device to; perhaps it
>> should be the caller in this case? That would make that caller domain
>> a pseudo-hwdom though, as far as PCI is concerned, which may not be
>> desirable according to my (limited) understanding of dom0less.
> 
> This is not really related to this patch but the plan is the following:
> - enumeration would have to be done by the firmware or boot loader before
> - xen will have some code to detect PCI devices
> - dom0less can be used to assign PCI devices to guest
> 
> Anyway does not change the fact that this must be called when domain is
> not NULL and I will fix that.

Since we now all seem to agree that the NULL would have been a problem,
may I ask in how far any of this has actually been tested?

Jan