Re: [PATCH v4 00/11] virtio-iommu: Add ACPI support

[Jean-Philippe Brucker]

Hi Haiwei,

On Mon, Oct 11, 2021 at 06:10:07PM +0800, Haiwei Li wrote:
[...]
> Gave up waiting for root file system device.  Common problems:
>  - Boot args (cat /proc/cmdline)
>    - Check rootdelay= (did the system wait long enough?)
>  - Missing modules (cat /proc/modules; ls /dev)
> ALERT!  UUID=3caf26b5-4d08-43e0-8634-7573269c4f70 does not exist.
> Dropping to a shell!
> 
> Any suggestions? Thanks.

It's possible that the rootfs is on a disk behind the IOMMU, and the IOMMU
driver doesn't get loaded. That could happen, for example, if the
virtio-iommu module is not present in the initramfs. Since IOMMU drivers
are typically built into the kernel rather than modules, distro tools that
build the initramfs might not pick up IOMMU modules. I'm guessing this
could be the issue here because of the hints and "Dropping to a shell"
line.

The clean solution will be to patch the initramfs tools to learn about
IOMMU drivers (I'm somewhat working on that). In the meantime, if this is
indeed the problem, you could try explicitly adding the virtio-iommu
module to the initramfs, or building the kernel with CONFIG_VIRTIO_IOMMU=y
rather than =m, though that requires VIRTIO and VIRTIO_PCI to be built-in
as well.

Thanks,
Jean