Re: [PATCH v2 10/11] vpci: Add initial support for virtual PCI bus topology

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

Hi, Jan!

Sorry for top posting, but this is a general question on this 
patch/functionality.

Do you see we need to gate all this with CONFIG_HAS_VPCI_GUEST_SUPPORT

as this renders in somewhat dead code for x86 for now? I do think this still

needs to be in the common code though.

Thank you in advance,

Oleksandr

On 28.09.21 15:58, Oleksandr Andrushchenko wrote:
> On 28.09.21 11:17, Michal Orzel wrote:
>> On 28.09.2021 09:59, Jan Beulich wrote:
>>> On 28.09.2021 09:48, Michal Orzel wrote:
>>>> On 23.09.2021 14:55, Oleksandr Andrushchenko wrote:
>>>>> --- a/xen/drivers/passthrough/pci.c
>>>>> +++ b/xen/drivers/passthrough/pci.c
>>>>> @@ -833,6 +833,63 @@ int pci_remove_device(u16 seg, u8 bus, u8 devfn)
>>>>>        return ret;
>>>>>    }
>>>>>    
>>>>> +static struct vpci_dev *pci_find_virtual_device(const struct domain *d,
>>>>> +                                                const struct pci_dev 
>>>>> *pdev)
>>>>> +{
>>>>> +    struct vpci_dev *vdev;
>>>>> +
>>>>> +    list_for_each_entry ( vdev, &d->vdev_list, list )
>>>>> +        if ( vdev->pdev == pdev )
>>>>> +            return vdev;
>>>>> +    return NULL;
>>>>> +}
>>>>> +
>>>>> +int pci_add_virtual_device(struct domain *d, const struct pci_dev *pdev)
>>>>> +{
>>>>> +    struct vpci_dev *vdev;
>>>>> +
>>>>> +    ASSERT(!pci_find_virtual_device(d, pdev));
>>>>> +
>>>>> +    /* Each PCI bus supports 32 devices/slots at max. */
>>>>> +    if ( d->vpci_dev_next > 31 )
>>>>> +        return -ENOSPC;
>>>>> +
>>>>> +    vdev = xzalloc(struct vpci_dev);
>>>>> +    if ( !vdev )
>>>>> +        return -ENOMEM;
>>>>> +
>>>>> +    /* We emulate a single host bridge for the guest, so segment is 
>>>>> always 0. */
>>>>> +    *(u16*) &vdev->seg = 0;
>>>> Empty line hear would improve readability due to the asterisks being so 
>>>> close to each other.
> Will add
>>>> Apart from that:
>>>> Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
>>>>> +    /*
>>>>> +     * The bus number is set to 0, so virtual devices are seen
>>>>> +     * as embedded endpoints behind the root complex.
>>>>> +     */
>>>>> +    *((u8*) &vdev->bus) = 0;
>>>>> +    *((u8*) &vdev->devfn) = PCI_DEVFN(d->vpci_dev_next++, 0);
>>> All of these casts are (a) malformed and (b) unnecessary in the first
>>> place, afaics at least.
>>>
>> Agree.
>> *((u8*) &vdev->bus) = 0;
>> is the same as:
>> vdev->bus = 0;
> Overengineering at its best ;)
>
> Will fix that
>
>>> Jan
>>>
> Thank you,
>
> Oleksandr