Re: [edk2-devel] [PATCH v1] OvmfPkg/PlatformInitLib: Don't override user specified PciMmio64Size

["Vivek Kasireddy" <vivek.kasireddy@intel.com>]

Hi Gerd,

> 
> > > Strictly speaking you don't care that much about the size of the mmio
> > > window, but where it gets placed.  Moving it to the end of the vcpu
> > > address space is what breaks your use case in case the iommu address
> > > space happens to be too small for that.
> > Right, the crux of the problem is indeed the placement of the window
> > and not the size. Given this, do you see any problem if the mmio window
> > were to be placed at the lower end of the address space?
> 
> That might still not work because OVMF scales the window size with the
> address space.
> 
> > Or, do you think
> > ensuring that PhysMemAddressWidth = <IOMMU address width>
> > automatically via Qemu/OVMF like Laszlo suggested is a better solution
> > for this problem?
> 
> The best temporary stop gap IMHO is using
> 
>   -cpu host-phys-bits=on,host-phys-bits-limit=<iommu-address-bits>
> 
> Side note: The qemu master branch has a precompiled seabios version
> which also does iommu window scaling and will need the same treatment.
> 
> How to solve that long-term should be discussed on the qemu-devel list.
Ok, I'll look into how this problem can be solved in Qemu and will further
discuss about this issue on qemu-devel.

Thanks,
Vivek

> 
> take care,
>   Gerd



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