Re: [PATCH] hvmloader/PCI: skip huge BARs in certain calculations

[Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>]

Hi,

On 04/03/2024 07:32, Jan Beulich wrote:
> BARs of size 2Gb and up can't possibly fit below 4Gb: Both the bottom of
> the lower 2Gb range and the top of the higher 2Gb range have special
> purpose. Don't even have them influence whether to (perhaps) relocate
> low RAM.
>
> Reported-by: Neowutran <xen@xxxxxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> If we wanted to fit e.g. multiple 1Gb BARs, it would likely be prudent
> to similarly avoid low RAM relocation in the first place. Yet accounting
> for things differently depending on how many large BARs there are would
> require more intrusive code changes.>
> That said, I'm open to further lowering of the threshold. That'll
> require different justification then, though.
>
GPUs without resizable BARs tend to expose 256MiB on the BAR regardless
of the amount of internal VRAM, AFAIK. So IMO 256 MiB is not a totally
unmotivated number. I don't know which other PCIe devices might expose
such big BARs for comparison.

Cheers,
Alejandro