Re: [PATCH v6 06/13] vpci/header: implement guest BAR register handlers

[Jan Beulich <jbeulich@xxxxxxxx>]

On 08.02.2022 10:57, Oleksandr Andrushchenko wrote:
> On 08.02.22 11:48, Jan Beulich wrote:
>> On 08.02.2022 10:31, Oleksandr Andrushchenko wrote:
>>> On 08.02.22 11:25, Roger Pau Monné wrote:
>>>> On Fri, Feb 04, 2022 at 08:34:52AM +0200, Oleksandr Andrushchenko wrote:
>>>>> @@ -516,6 +594,11 @@ static int init_bars(struct pci_dev *pdev)
>>>>>            if ( (val & PCI_BASE_ADDRESS_SPACE) == 
>>>>> PCI_BASE_ADDRESS_SPACE_IO )
>>>>>            {
>>>>>                bars[i].type = VPCI_BAR_IO;
>>>>> +
>>>>> +            rc = bar_ignore_access(pdev, reg, &bars[i]);
>>>> This is wrong: you only want to ignore access to IO BARs for Arm, for
>>>> x86 we should keep the previous behavior. Even more if you go with
>>>> Jan's suggestions to make bar_ignore_access also applicable to dom0.
>>> How do we want this?
>>> #ifdef CONFIG_ARM?
>> Afaic better via a new, dedicated CONFIG_HAVE_* setting, which x86 selects
>> but Arm doesn't. Unless we have one already, of course ...
> Could you please be more specific on the name you see appropriate?

I'm pretty sure Linux has something similar, so I'd like to ask that
you go look there. I'm sorry to say this a little bluntly, but I'm
really in need of doing something beyond answering your mails (and
in part re-stating the same thing again and again).

> And do you realize that this is going to be a single user of such a
> setting?

Yes, but I'm not sure this is going to remain just a single use.
Furthermore every CONFIG_<arch> is problematic as soon as a new port
is being worked on. If we wanted to go with a CONFIG_<arch> here, imo
it ought to be CONFIG_X86, not CONFIG_ARM, as I/O ports are really an
x86-specific thing (which has propagated into other architectures in
more or less strange ways, but never as truly I/O ports).

Jan