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

[Laszlo Ersek <lersek@redhat.com>]

On 06/17/20 08:40, Gerd Hoffmann wrote:
>   Hi,
> 
>> What if then we have OVMF relying in the physbits *iff*
>> "-host-phys-bits" is used
> 
> How can the guest know?

Exactly!

> Adding "you can trust physbits" bits somewhere (as suggested by Eduardo)
> would work for sure, but would depend on a qemu update.
> 
> Maybe a "don't trust physbits in case it is 40" heuristic works well
> enough in practice.

... for how many years? ;)

No heuristics please.

(I absolutely prefer X-PciMmio64Mb to guesswork. With X-PciMmio64Mb,
users at least know they have to be careful. I know they don't like
that, they just want a promise "it will work forever", but it's not
randomly called "experimental", we're not there just yet.)

Thank you,
Laszlo

>> Now, regarding the problem "to trust or not" in the guests' physbits,
>> I think it's an orthogonal discussion to some extent.
> 
> It isn't.  OVMF can't ignore the problem, you risk to break guests if
> you do.
> 
> take care,
>   Gerd
>