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

From: Jan Beulich <jbeulich@suse.com>
To: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>,
	Oleksandr Andrushchenko <andr2000@gmail.com>
Cc: "Rahul.Singh@arm.com" <Rahul.Singh@arm.com>,
	"Bertrand.Marquis@arm.com" <Bertrand.Marquis@arm.com>,
	"julien.grall@arm.com" <julien.grall@arm.com>,
	"sstabellini@kernel.org" <sstabellini@kernel.org>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	"iwj@xenproject.org" <iwj@xenproject.org>,
	"wl@xen.org" <wl@xen.org>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH 02/10] arm/pci: Maintain PCI assignable list
Date: Wed, 11 Nov 2020 16:25:20 +0100	[thread overview]
Message-ID: <4619f6b5-6050-6beb-ced7-f7d6da9782d0@suse.com> (raw)
In-Reply-To: <d94e37a3-d8b3-7d3d-0ba5-c7885a5ef512@epam.com>

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@epam.com>
>>>>>
>>>>> 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