[PATCH 3/5] iommu: Add return errno rules to ->attach_dev ops

Nicolin Chen
2022-09-13T08:29:20Z

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 EINVAL from the IOMMU driver during attach that
the reason attached failed is because of domain incompatability.

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 kdocs first to add rules of return errno to ->attach_dev ops.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
include/linux/iommu.h | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ea30f00dc145..c5d7ec0187c7 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -266,6 +266,17 @@ struct iommu_ops {
/**
* struct iommu_domain_ops - domain specific operations
* @attach_dev: attach an iommu domain to a device
+ * Rules of its return errno:
+ * EINVAL - Exclusively, device and domain are incompatible. Must
+ * avoid kernel prints along with this errno. Any EINVAL
+ * returned from kAPIs must be converted to ENODEV if it
+ * is device-specific, or to some other reasonable errno
+ * being listed below
+ * ENOMEM - Out of memory
+ * ENOSPC - No space left on device
+ * EBUSY - Device is attached to a domain and cannot be changed
+ * ENODEV - Device specific errors, not able to be attached
+ * <others> - Treated as ENODEV by the caller. Use is discouraged
* @detach_dev: detach an iommu domain from a device
* @map: map a physically contiguous memory region to an iommu domain
* @map_pages: map a physically contiguous set of pages of the same size to
--
2.17.1