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

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Date:   Fri, 29 Jul 2022 14:30:49 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     joro@...tes.org, will@...nel.org, marcan@...can.st,
        sven@...npeter.dev, robin.murphy@....com, robdclark@...il.com,
        baolu.lu@...ux.intel.com, orsonzhai@...il.com,
        baolin.wang7@...il.com, zhang.lyra@...il.com,
        jean-philippe@...aro.org, alex.williamson@...hat.com,
        kevin.tian@...el.com, suravee.suthikulpanit@....com,
        alyssa@...enzweig.io, dwmw2@...radead.org, mjrosato@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, thierry.reding@...il.com,
        vdumpa@...dia.com, jonathanh@...dia.com, cohuck@...hat.com,
        thunder.leizhen@...wei.com, christophe.jaillet@...adoo.fr,
        chenxiang66@...ilicon.com, john.garry@...wei.com,
        yangyingliang@...wei.com, iommu@...ts.linux-foundation.org,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        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
Subject: Re: [PATCH v5 1/5] iommu: Return -EMEDIUMTYPE for incompatible
 domain and device/group

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@...dia.com>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.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@...dia.com>

Jason