linux-kernel - Re: [PATCH v4 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

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Date:   Fri, 1 Jul 2022 14:53:13 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Nicolin Chen <nicolinc@...dia.com>, joro@...tes.org,
        will@...nel.org, marcan@...can.st, sven@...npeter.dev,
        robin.murphy@....com, robdclark@...il.com, orsonzhai@...il.com,
        baolin.wang7@...il.com, zhang.lyra@...il.com,
        jean-philippe@...aro.org, alex.williamson@...hat.com,
        jgg@...dia.com, kevin.tian@...el.com
Cc:     baolu.lu@...ux.intel.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 v4 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain
 and device/group

On 2022/7/1 04:36, 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>
> Signed-off-by: Nicolin Chen<nicolinc@...dia.com>

Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>

Best regards,
baolu