Re: [PATCH v5 10/14] vpci/header: reset the command register when adding devices

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

Hi, Roger!

On 13.01.22 13:07, Roger Pau Monné wrote:
> On Thu, Nov 25, 2021 at 01:02:47PM +0200, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>
>> Reset the command register when passing through a PCI device:
>> it is possible that when passing through a PCI device its memory
>> decoding bits in the command register are already set. Thus, a
>> guest OS may not write to the command register to update memory
>> decoding, so guest mappings (guest's view of the BARs) are
>> left not updated.
>>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>> ---
>> Since v1:
>>   - do not write 0 to the command register, but respect host settings.
> There's not much respect of host setting here, are you are basically
> writing 0 except for the INTX_DISABLE which will be set if MSI(X) is
> enabled.
Yes, and this is because we only support INTX emulation at the
moment
>
> I wonder whether you really need this anyway. I would expect that a
> device that's being assigned to a guest has just been reset globally,
> so there should be no need to reset the command register explicitly.
 From my experience it was a real case when the device was not
reset making troubles. I'll remove this patch for now and see if
I can still run without it relying on the device reset which must
be in place while assigning a PCI device (here we rely on the
toolstack, right?).
>
> Thanks, Roger.
Thank you,
Oleksandr