Re: [PATCH v4 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

[Baolu Lu]

On 2022/7/1 04:36, Nicolin Chen wrote:
> Cases like VFIO wish to attach a device to an existing domain that was
> not allocated specifically from the device. This raises a condition
> where the IOMMU driver can fail the domain attach because the domain and
> device are incompatible with each other.
>
> This is a soft failure that can be resolved by using a different domain.
>
> Provide a dedicated errno from the IOMMU driver during attach that the
> reason attached failed is because of domain incompatability. EMEDIUMTYPE
> is chosen because it is never used within the iommu subsystem today and
> evokes a sense that the 'medium' aka the domain is incompatible.
>
> VFIO can use this to know attach is a soft failure and it should continue
> searching. Otherwise the attach will be a hard failure and VFIO will
> return the code to userspace.
>
> Update all drivers to return EMEDIUMTYPE in their failure paths that are
> related to domain incompatability. Also remove adjacent error prints for
> these soft failures, to prevent a kernel log spam, since -EMEDIUMTYPE is
> clear enough to indicate an incompatability error.
>
> Add kdocs describing this behavior.
>
> Suggested-by: Jason Gunthorpe<jgg@xxxxxxxxxx>
> Reviewed-by: Kevin Tian<kevin.tian@xxxxxxxxx>
> Signed-off-by: Nicolin Chen<nicolinc@xxxxxxxxxx>

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

Best regards,
baolu