RE: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable nested SMMUv3

[Shameerali Kolothum Thodi via <qemu-devel@nongnu.org>]

> -----Original Message-----
> From: Nathan Chen <nathanc@nvidia.com>
> Sent: Saturday, January 25, 2025 2:44 AM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
> Cc: ddutile@redhat.com; eric.auger@redhat.com; jgg@nvidia.com;
> jiangkunkun <jiangkunkun@huawei.com>; Jonathan Cameron
> <jonathan.cameron@huawei.com>; Linuxarm <linuxarm@huawei.com>;
> nathanc@nvidia.com; nicolinc@nvidia.com; peter.maydell@linaro.org;
> qemu-arm@nongnu.org; Wangzhou (B) <wangzhou1@hisilicon.com>;
> zhangfei.gao@linaro.org; qemu-devel@nongnu.org
> Subject: RE: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable
> nested SMMUv3
> 
> >>  >with an error message indicating DMA mapping failed for the
> >> passthrough >devices.
> >>
> >> A correction - the message indicates UEFI failed to find a mapping for
> >> the boot partition ("map: no mapping found"), not that DMA mapping
> >> failed. But earlier EDK debug logs still show PCI host bridge resource
> >> conflicts for the passthrough devices that seem related to the VM boot
> >> failure.
> >
> > I have tried a 2023 version EFI which works. And for more recent tests I
> am
> > using a one built directly from,
> > https://github.com/tianocore/edk2.git master
> >
> > Commit: 0f3867fa6ef0("UefiPayloadPkg/UefiPayloadEntry: Fix PT
> protection
> > in 5 level paging"
> >
> > With both, I don’t remember seeing any boot failure and the above UEFI
> > related "map: no mapping found" error. But the Guest kernel at times
> > complaints about pci bridge window memory assignment failures.
> > ...
> > pci 0000:10:01.0: bridge window [mem size 0x00200000 64bit pref]: can't
> assign; no space
> > pci 0000:10:01.0: bridge window [mem size 0x00200000 64bit pref]: failed
> to assign
> > pci 0000:10:00.0: bridge window [io  size 0x1000]:can't assign; no space
> > ...
> >
> > But Guest still boots and worked fine so far.
> 
> Hi Shameer,
> 
> Just letting you know I resolved this by increasing the MMIO region size
> in hw/arm/virt.c to support passing through GPUs with large BAR regions
> (VIRT_HIGH_PCIE_MMIO). Thanks for taking a look.
> 

Ok. Thanks for that. Does that mean may be an optional property to specify
the size for VIRT_HIGH_PCIE_MMIO is worth adding?

And for the PCI bridge window specific errors that I mentioned above,

>>pci 0000:10:01.0: bridge window [mem size 0x00200000 64bit pref]: can't assign; no space

adding  ""mem-reserve=X" and "io-reserve=X" to pcie-root-port helps.

Thanks,
Shameer