Re: [PATCH 08/10] vpci/arm: Allow updating BAR's header for non-ECAM bridges

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.11.2020 11:39, Oleksandr Andrushchenko wrote:
> 
> On 11/13/20 12:29 PM, Jan Beulich wrote:
>> On 09.11.2020 13:50, Oleksandr Andrushchenko wrote:
>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>>
>>> Non-ECAM host bridges in hwdom go directly to PCI config space,
>>> not through vpci (they use their specific method for accessing PCI
>>> configuration, e.g. dedicated registers etc.).
>> And access to these dedicated registers can't be intercepted?
> 
> It can. But then you have to fully emulate that bridge, e.g.
> 
> "if we write A to regB and after that write C to regZ then it
> 
> means we are accessing config space. If we write...."

Sounds pretty much like the I/O port based access mechanism on
x86, which also has some sort of "enable". Of course, I/O port
accesses are particularly easy to intercept and handle...

> I mean this would need lots of code in Xen to achieve that

Possibly, but look at the amount of code we have in Xen on the
x86 side to handle MCFG writes by Dom0.

Jan