> From: Nicolin Chen <nicolinc@xxxxxxxxxx> > Sent: Thursday, June 16, 2022 8:03 AM > > 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 turn adjacent error prints into > debug prints, for these soft failures, to prevent a kernel log spam. > > Add kdocs describing this behavior. > > Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx> > Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
