linux-kernel - [PATCH v2 03/13] iommu: Add return value rules to attach

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Message-ID: <20220914051234.10006-2-nicolinc@nvidia.com>
Date:   Tue, 13 Sep 2022 22:12:34 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     <joro@...tes.org>, <suravee.suthikulpanit@....com>,
        <will@...nel.org>, <robin.murphy@....com>, <robdclark@...il.com>,
        <dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>,
        <agross@...nel.org>, <bjorn.andersson@...aro.org>,
        <konrad.dybcio@...ainline.org>, <matthias.bgg@...il.com>,
        <heiko@...ech.de>, <orsonzhai@...il.com>,
        <baolin.wang@...ux.alibaba.com>, <zhang.lyra@...il.com>,
        <thierry.reding@...il.com>, <jean-philippe@...aro.org>,
        <jgg@...dia.com>, <sricharan@...eaurora.org>
CC:     <yong.wu@...iatek.com>, <vdumpa@...dia.com>,
        <jonathanh@...dia.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>,
        <linux-arm-kernel@...ts.infradead.org>,
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Subject: [PATCH v2 03/13] iommu: Add return value rules to attach_dev op

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 value to the attach_dev op.

Suggested-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Nicolin Chen <nicolinc@...dia.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..aacf9a2b151f 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
+ *  Return:
+ * * 0		- success
+ * * EINVAL	- exclusively, device and domain are incompatible. Must avoid
+ *		  kernel prints along with this errno. Any EINVAL returned from
+ *		  a kAPI 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