Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture

[Guilherme Piccoli]

On Wed, Jun 17, 2020 at 12:57 PM Laszlo Ersek <lersek@redhat.com> wrote:
> [...]
> I don't necessarily see compat issues -- large-BAR PCI device assignment
> might simply stop working under those circumstances, because you could
> no longer use X-PciMmio64Mb, and the new way wouldn't be supported by
> (old) QEMU.
>
> This would indeed be a regression relative to "X-PciMmio64Mb", but
> that's exactly why there's an "X" in "X-PciMmio64Mb".
>

Are you planning to remove that option, with this improvement? I think
we could keep it for a while, as a way to override the automatic
mechanism we might implement. This is even for "safe" purposes, in
case there's some corner case with the auto-sized aperture that we
ignore upfront.

> > So, the code may be a bit complex, it'll
> > need to take into account this case (probably we could just rely on
> > the physbits "detected" by OVMF in such case, limiting PCI64 aperture
> > to the current 36-bits, right?).
>
> A "bit complex" is an understatement. The code is already much more
>[...]
heheh
indeed, it's very complex code! It took me a while to even start to
figure where things are done, I guess UEFI spec is complex in nature
too, which adds to that code complexity!