Re: [PATCH v2] target/i386/host-cpu: Use iommu phys_bits with VFIO assigned devices on Intel h/w

[Laszlo Ersek]

On 1/18/24 20:20, Vivek Kasireddy wrote:
> Recent updates in OVMF and Seabios have resulted in MMIO regions
> being placed at the upper end of the physical address space. As a
> result, when a Host device is assigned to the Guest via VFIO, the
> following mapping failures occur when VFIO tries to map the MMIO
> regions of the device:
> VFIO_MAP_DMA failed: Invalid argument
> vfio_dma_map(0x557b2f2736d0, 0x380000000000, 0x1000000, 0x7f98ac400000) = -22 
> (Invalid argument)
> 
> The above failures are mainly seen on some Intel platforms where
> the physical address width is larger than the Host's IOMMU
> address width. In these cases, VFIO fails to map the MMIO regions
> because the IOVAs would be larger than the IOMMU aperture regions.
> 
> Therefore, one way to solve this problem would be to ensure that
> cpu->phys_bits = <IOMMU phys_bits>
> This can be done by parsing the IOMMU caps value from sysfs and
> extracting the address width and using it to override the
> phys_bits value as shown in this patch.
> 
> Previous attempt at solving this issue in OVMF:
> https://edk2.groups.io/g/devel/topic/102359124
> 
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Cédric Le Goater <clg@redhat.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Dongwon Kim <dongwon.kim@intel.com>
> Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> Tested-by: Yanghang Liu <yanghliu@redhat.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
> 
> ---
> v2:
> - Replace the term passthrough with assigned (Laszlo)

v1 of the patch was posted in last November; I've now re-read my
(superficial) comments from back then.

Acked-by: Laszlo Ersek <lersek@redhat.com>