Re: [PATCH v2 8/9] vfio: Check compatibility of CPU and IOMMU address space width

["Daniel Kral" <d.kral@proxmox.com>]

On Thu Jan 30, 2025 at 2:43 PM CET, Cédric Le Goater wrote:
> Print a warning if IOMMU address space width is smaller than the
> physical address width. In this case, PCI peer-to-peer transactions on
> BARs are not supported and failures of device MMIO regions are to be
> expected.
>
> This can occur with the 39-bit IOMMU address space width as found on
> consumer grade processors or when using a vIOMMU device with default
> settings.
>
> Signed-off-by: Cédric Le Goater <clg@redhat.com>

Hi Cédric!

Some of our users are running into this with Proxmox VE, where they get
vfio_container_dma_map(...) = -22 errors, which are likely caused by
this issue of the mismatch mentioned above. Setting the guest-phys-bits
in accordance to the iommu aw-bits seems to fix that for users, e.g.
[0].

Before applying this downstream for pve-qemu, I saw that this patch was
dropped in the v3 [1], but you mentioned that this is addressed in a
later series. I couldn't find a direct follow-up in the archive, are
there any updates on this?

Thanks a lot in advance & have a nice weekend!

    Daniel


[0] https://forum.proxmox.com/threads/169586/page-3#post-795813
[1] https://lore.kernel.org/qemu-devel/20250206131438.1505542-1-clg@redhat.com/