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

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Date:   Thu, 8 Sep 2022 20:17:23 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...dia.com>
CC:     <will@...nel.org>, <robin.murphy@....com>,
        <alex.williamson@...hat.com>, <suravee.suthikulpanit@....com>,
        <marcan@...can.st>, <sven@...npeter.dev>, <alyssa@...enzweig.io>,
        <robdclark@...il.com>, <dwmw2@...radead.org>,
        <baolu.lu@...ux.intel.com>, <mjrosato@...ux.ibm.com>,
        <gerald.schaefer@...ux.ibm.com>, <orsonzhai@...il.com>,
        <baolin.wang@...ux.alibaba.com>, <zhang.lyra@...il.com>,
        <thierry.reding@...il.com>, <vdumpa@...dia.com>,
        <jonathanh@...dia.com>, <jean-philippe@...aro.org>,
        <cohuck@...hat.com>, <tglx@...utronix.de>,
        <shameerali.kolothum.thodi@...wei.com>,
        <thunder.leizhen@...wei.com>, <christophe.jaillet@...adoo.fr>,
        <yangyingliang@...wei.com>, <jon@...id-run.com>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        <asahi@...ts.linux.dev>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-s390@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>, <kvm@...r.kernel.org>,
        <kevin.tian@...el.com>
Subject: Re: [PATCH v6 1/5] iommu: Return -EMEDIUMTYPE for incompatible
 domain and device/group

On Thu, Sep 08, 2022 at 01:14:42PM -0300, Jason Gunthorpe wrote:

> > I am wondering if this can be solved by better defining what the return
> > codes mean and adjust the call-back functions to match the definition.
> > Something like:
> > 
> > 	-ENODEV : Device not mapped my an IOMMU
> > 	-EBUSY  : Device attached and domain can not be changed
> > 	-EINVAL : Device and domain are incompatible
> > 	...
> 
> Yes, this was gone over in a side thread the pros/cons, so lets do
> it. Nicolin will come with something along these lines.

I have started this effort by combining this list and the one from
the side thread:

@@ -266,6 +266,13 @@ struct iommu_ops {
 /**
  * struct iommu_domain_ops - domain specific operations
  * @attach_dev: attach an iommu domain to a device
+ *              Rules of its return errno:
+ *               ENOMEM  - Out of memory
+ *               EINVAL  - Device and domain are incompatible
+ *               EBUSY   - Device is attached to a domain and cannot be changed
+ *               ENODEV  - Device or domain is messed up: device is not mapped
+ *                         to an IOMMU, no domain can attach, and etc.
+ *              <others> - Same behavior as ENODEV, 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

I am now going through every single return value of ->attach_dev to
make sure the list above applies. And I will also incorporate things
like Robin's comments at the AMD IOMMU driver.

And if the change occurs to be bigger, I guess that separating it to
be an IOMMU series from this VFIO one might be better.

Thanks
Nic