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Date:   Mon, 12 Sep 2022 22:07:37 -0700
From:   Nicolin Chen <nicolinc@nvidia.com>
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Subject: Re: [PATCH v6 1/5] iommu: Return -EMEDIUMTYPE for incompatible
 domain and device/group
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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