Re: [edk2-devel] [BUG] Extremely slow boot times with CPU and GPU passthrough and host phys-bits > 40

["Gerd Hoffmann via groups.io" <kraxel=redhat.com@groups.io>]

On Sat, Nov 23, 2024 at 06:05:40PM -0800, mitchell.augustin via groups.io wrote:
> Hi again,
> I have a more specific version of a prior question: Is there some
> fw_cfg flag that would simply allow me to use the classic MMIO window,
> in effect keeping PlatformInfoHob->PcdPciMmio64Size and
> PlatformInfoHob->PcdPciMmio64Base set to what they would be with the
> PlatformDynamicMmioWindow patch (
> https://github.com/tianocore/edk2/commit/ecb778d0ac62560aa172786ba19521f27bc3f650
> ) disabled?

Not directly.  OVMF considers PcdPciMmio64Size being the minimum size.
Rf the dynamic mmio window would be larger it will simply use the
dynamic mmio window, otherwise the PcdPciMmio64Size + PcdPciMmio64Base
values.

The dynamic mmio windos is 1/8 of the address space, i.e. for
phys-bits=42 (4TB address space) the dynamic mmio window size is 512GB.
In that case you can set PcdPciMmio64Size to 1TB and PcdPciMmio64Base to
1 or 2 or 3 TB and OVMF should use these values.

take care,
  Gerd



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