Re: [PATCH v5 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

From: Jason Gunthorpe <jgg@nvidia.com>
To: Nicolin Chen <nicolinc@nvidia.com>
Cc: joro@8bytes.org, will@kernel.org, marcan@marcan.st,
	sven@svenpeter.dev, robin.murphy@arm.com, robdclark@gmail.com,
	baolu.lu@linux.intel.com, orsonzhai@gmail.com,
	baolin.wang7@gmail.com, zhang.lyra@gmail.com,
	jean-philippe@linaro.org, alex.williamson@redhat.com,
	kevin.tian@intel.com, suravee.suthikulpanit@amd.com,
	alyssa@rosenzweig.io, dwmw2@infradead.org,
	mjrosato@linux.ibm.com, gerald.schaefer@linux.ibm.com,
	thierry.reding@gmail.com, vdumpa@nvidia.com,
	jonathanh@nvidia.com, cohuck@redhat.com,
	thunder.leizhen@huawei.com, christophe.jaillet@wanadoo.fr,
	chenxiang66@hisilicon.com, john.garry@huawei.com,
	yangyingliang@huawei.com, iommu@lists.linux-foundation.org,
	iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-arm-msm@vger.kernel.org, linux-s390@vger.kernel.org,
	linux-tegra@vger.kernel.org,
	virtualization@lists.linux-foundation.org, kvm@vger.kernel.org
Subject: Re: [PATCH v5 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group
Date: Fri, 29 Jul 2022 14:30:49 -0300	[thread overview]
Message-ID: <YuQZSfQtBTBtJOq2@nvidia.com> (raw)
In-Reply-To: <20220701214455.14992-2-nicolinc@nvidia.com>

On Fri, Jul 01, 2022 at 02:44:51PM -0700, Nicolin Chen wrote:
> 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 from the IOMMU driver during attach that the
> reason attached failed is because of domain incompatability. EMEDIUMTYPE
> is chosen because it is never used within the iommu subsystem today and
> evokes a sense that the 'medium' aka the domain is incompatible.
> 
> 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 all drivers to return EMEDIUMTYPE in their failure paths that are
> related to domain incompatability. Also remove adjacent error prints for
> these soft failures, to prevent a kernel log spam, since -EMEDIUMTYPE is
> clear enough to indicate an incompatability error.
> 
> Add kdocs describing this behavior.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>  drivers/iommu/amd/iommu.c                   |  2 +-
>  drivers/iommu/apple-dart.c                  |  4 +--
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 15 +++--------
>  drivers/iommu/arm/arm-smmu/arm-smmu.c       |  5 +---
>  drivers/iommu/arm/arm-smmu/qcom_iommu.c     |  9 ++-----
>  drivers/iommu/intel/iommu.c                 | 10 +++-----
>  drivers/iommu/iommu.c                       | 28 +++++++++++++++++++++
>  drivers/iommu/ipmmu-vmsa.c                  |  4 +--
>  drivers/iommu/omap-iommu.c                  |  3 +--
>  drivers/iommu/s390-iommu.c                  |  2 +-
>  drivers/iommu/sprd-iommu.c                  |  6 ++---
>  drivers/iommu/tegra-gart.c                  |  2 +-
>  drivers/iommu/virtio-iommu.c                |  3 +--
>  13 files changed, 47 insertions(+), 46 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason