Re: [PATCH 02/10] arm/pci: Maintain PCI assignable list

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.11.2020 16:13, Oleksandr Andrushchenko wrote:
> On 11/11/20 5:03 PM, Roger Pau Monné wrote:
>> On Wed, Nov 11, 2020 at 02:38:47PM +0000, Oleksandr Andrushchenko wrote:
>>> On 11/11/20 3:53 PM, Roger Pau Monné wrote:
>>>> On Mon, Nov 09, 2020 at 02:50:23PM +0200, Oleksandr Andrushchenko wrote:
>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>>>>
>>>>> The original code depends on pciback to manage assignable device list.
>>>>> The functionality which is implemented by the pciback and the toolstack
>>>>> and which is relevant/missing/needed for ARM:
>>>>>
>>>>> 1. pciback is used as a database for assignable PCI devices, e.g. xl
>>>>>      pci-assignable-{add|remove|list} manipulates that list. So, whenever 
>>>>> the
>>>>>      toolstack needs to know which PCI devices can be passed through it 
>>>>> reads
>>>>>      that from the relevant sysfs entries of the pciback.
>>>>>
>>>>> 2. pciback is used to hold the unbound PCI devices, e.g. when passing 
>>>>> through
>>>>>      a PCI device it needs to be unbound from the relevant device driver 
>>>>> and bound
>>>>>      to pciback (strictly speaking it is not required that the device is 
>>>>> bound to
>>>>>      pciback, but pciback is again used as a database of the passed 
>>>>> through PCI
>>>>>      devices, so we can re-bind the devices back to their original 
>>>>> drivers when
>>>>>      guest domain shuts down)
>>>>>
>>>>> 1. As ARM doesn't use pciback implement the above with additional sysctls:
>>>>>    - XEN_SYSCTL_pci_device_set_assigned
>>>> I don't see the point in having this sysfs, Xen already knows when a
>>>> device is assigned because the XEN_DOMCTL_assign_device hypercall is
>>>> used.
>>> But how does the toolstack know about that? When the toolstack needs to
>>>
>>> list/know all assigned devices it queries pciback's sysfs entries. So, with
>>>
>>> XEN_DOMCTL_assign_device we make that knowledge available to Xen,
>>>
>>> but there are no means for the toolstack to get it back.
>> But the toolstack will figure out whether a device is assigned or
>> not by using
>> XEN_SYSCTL_pci_device_get_assigned/XEN_SYSCTL_pci_device_enum_assigned?
>>
>> AFAICT XEN_SYSCTL_pci_device_set_assigned tells Xen a device has been
>> assigned, but Xen should already know it because
>> XEN_DOMCTL_assign_device would have been used to assign the device?
> 
> Ah, I misunderstood you then. So, we only want to drop 
> XEN_DOMCTL_assign_device
> 
> and keep the rest.

Was this a typo? Why would you want to drop XEN_DOMCTL_assign_device?

Jan