Re: [PATCH v6 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

Nicolin Chen
2022-09-13T05:07:49Z

On Tue, Sep 13, 2022 at 02:22:17AM +0000, Tian, Kevin wrote:
> External email: Use caution opening links or attachments
>
>
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Friday, September 9, 2022 8:08 PM
> >
> >
> > > As discussed in a side thread a note might be added to exempt calling
> > > kAPI outside of the iommu driver.
> >
> > Sadly, not really.. The driver is responsible to santize this if it is
> > relevant. It is the main downside of this approach.
> >
>
> Better provide a clarification on what sanitization means.
>
> e.g. I don't think we should change errno in those kAPIs to match the
> definition in iommu subsystem since e.g. -EINVAL really means different
> things in different context.
>
> So the sanitization in iommu driver is probably that:
>
> - If an external kAPI returns -EINVAL, convert it to -ENODEV given iommu
> domain is iommu internal object hence unlikely for external kAPIs to
> capture incompatibility issue between domain/device;
> - Otherwise just pass whatever returned to the caller, following the definition
> of "Same behavior as -ENODEV" above

I added something similar. Thanks!

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ea30f00dc145..190647d018f9 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. An EINVAL
+ * returned from a kAPI must be coverted 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