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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

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.

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.

Thanks, Roger.