Re: [PATCH] hvmloader: probe memory below 4G before allocation for OVMF

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 03/04/2020 16:28, Jan Beulich wrote:
> On 03.04.2020 17:17, Igor Druzhinin wrote:
>> On 03/04/2020 16:05, Jan Beulich wrote:
>>> On 03.04.2020 16:47, Igor Druzhinin wrote:
>>>> There multiple technical complications that caused this mess.
>>>> One of them is that there is no unfortunately a better place for the
>>>> framebuffer to be located initially. Second, SR-IOV device
>>>> is real and adding a virtual BAR to it is also complicated (due to
>>>> compatibility reasons) and NVIDIA decided to avoid that.
>>>
>>> In which case I wonder - aren't you ending up with the MMIO case
>>> that I had mentioned, and that you said is difficult to deal with?
>>
>> No, it's VRAM area (normal RAM pages) - not MMIO.
> 
> Well, VRAM is still MMIO from the CPU's perspective, just without
> any side effects. But if it was another device that was passed
> through, couldn't its MMIO similarly end up in that area?

As Andrew said, Xen VRAM is just normal RAM. It's originally
populated in this area for the lack of a better place (at least now).
It's special and has nothing to do with the device passed through
using conventional PCI mechanisms which BARs will only occupy MMIO hole.

Igor