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Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture
From: |
Christophe de Dinechin |
Subject: |
Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture |
Date: |
Wed, 17 Jun 2020 10:16:55 +0200 |
> Le 16 Jun 2020 à 18:50, Gerd Hoffmann <kraxel@redhat.com> a écrit :
>
> Hi,
>
>> (a) We could rely in the guest physbits to calculate the PCI64 aperture.
>
> I'd love to do that. Move the 64-bit I/O window as high as possible and
> use -- say -- 25% of the physical address space for it.
>
> Problem is we can't.
Is the only reason unreliable guest physbits?
>
>> failure. Also, if the users are not setting the physbits in the guest,
>> there must be a default (seems to be 40bit according to my experiments),
>> seems to be a good idea to rely on that.
>
> Yes, 40 is the default, and it is used *even if the host supports less
> than that*. Typical values I've seen for intel hardware are 36 and 39.
> 39 is used even by recent hardware (not the xeons, but check out a
> laptop or a nuc).
>
>> If guest physbits is 40, why to have OVMF limiting it to 36, right?
>
> Things will explode in case OVMF uses more physbits than the host
> supports (host physbits limit applies to ept too). In other words: OVMF
> can't trust the guest physbits, so it is conservative to be on the safe
> side.
>
> If we can somehow make a *trustable* physbits value available to the
> guest, then yes, we can go that route. But the guest physbits we have
> today unfortunately don't cut it.
What is the rationale for ever allowing guest physbits > host physbits?
>
> take care,
> Gerd
>
>
- Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture, (continued)
- Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture, Eduardo Habkost, 2020/06/17
- Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture, Dr. David Alan Gilbert, 2020/06/19
- Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture, Laszlo Ersek, 2020/06/17
- Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture, Laszlo Ersek, 2020/06/17
- Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture, Eduardo Habkost, 2020/06/17
- Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture, Laszlo Ersek, 2020/06/18
Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture,
Christophe de Dinechin <=