linux-kernel - Re: [PATCH v5 3/6] iommu: Add return value rules to attach

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Message-ID: <Yyyaar/DpXSboA2q@nvidia.com>
Date:   Thu, 22 Sep 2022 14:24:58 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     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, matthias.bgg@...il.com,
        orsonzhai@...il.com, baolin.wang@...ux.alibaba.com,
        zhang.lyra@...il.com, jean-philippe@...aro.org,
        sricharan@...eaurora.org, kevin.tian@...el.com,
        quic_jjohnson@...cinc.com, konrad.dybcio@...ainline.org,
        yong.wu@...iatek.com, thierry.reding@...il.com, vdumpa@...dia.com,
        jonathanh@...dia.com, tglx@...utronix.de,
        shameerali.kolothum.thodi@...wei.com,
        christophe.jaillet@...adoo.fr, thunder.leizhen@...wei.com,
        quic_saipraka@...cinc.com, jon@...id-run.com,
        yangyingliang@...wei.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-tegra@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v5 3/6] iommu: Add return value rules to attach_dev op
 and APIs

On Thu, Sep 22, 2022 at 01:54:08AM -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 EINVAL from the IOMMU driver during attach that
> the reason why the attach failed is because of domain incompatibility.
> 
> VFIO can use this to know that the 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 to add rules of return value to the attach_dev op and APIs.
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
>  drivers/iommu/iommu.c | 24 ++++++++++++++++++++++++
>  include/linux/iommu.h | 12 ++++++++++++
>  2 files changed, 36 insertions(+)

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

Jason