Re: [PATCH v5 06/14] vpci/header: implement guest BAR register handlers

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

Hi, Bertrand!

On 26.11.21 14:19, Oleksandr Andrushchenko wrote:
> Hi, Bertrand!
>
> On 25.11.21 18:28, Bertrand Marquis wrote:
>> Hi Oleksandr,
>>
>>> On 25 Nov 2021, at 11:02, Oleksandr Andrushchenko <andr2000@xxxxxxxxx> 
>>> wrote:
>>>
>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>>
>>> Add relevant vpci register handlers when assigning PCI device to a domain
>>> and remove those when de-assigning. This allows having different
>>> handlers for different domains, e.g. hwdom and other guests.
>>>
>>> Emulate guest BAR register values: this allows creating a guest view
>>> of the registers and emulates size and properties probe as it is done
>>> during PCI device enumeration by the guest.
>>>
>>> ROM BAR is only handled for the hardware domain and for guest domains
>>> there is a stub: at the moment PCI expansion ROM handling is supported
>>> for x86 only and it might not be used by other architectures without
>>> emulating x86. Other use-cases may include using that expansion ROM before
>>> Xen boots, hence no emulation is needed in Xen itself. Or when a guest
>>> wants to use the ROM code which seems to be rare.
>> In the generic code, bars for ioports are actually skipped (check code before
>> in header.c, in case of ioports there is a continue) and no handler is 
>> registered for them.
>> The consequence will be that a guest will access hardware when reading those 
>> BARs.
> Yes, this seems to be a valid point
So, with the approach we have developed these days we will ignore all writes
and return ~0 for reads for all unhandled ops, e.g. those which do not have 
explicit
register handlers employed. Thus, this case will fall into unhandled clause.

Thank you,
Oleksandr