Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Received-SPF: Pass (protection.outlook.com: domain of nvidia.com designates
 12.22.5.235 as permitted sender) receiver=protection.outlook.com;
 client-ip=12.22.5.235; helo=mail.nvidia.com; pr=C
Date:   Tue, 13 Sep 2022 13:14:24 -0700
From:   Nicolin Chen <nicolinc@nvidia.com>
To:     Jean-Philippe Brucker <jean-philippe@linaro.org>
CC:     <joro@8bytes.org>, <suravee.suthikulpanit@amd.com>,
        <will@kernel.org>, <robin.murphy@arm.com>, <robdclark@gmail.com>,
        <dwmw2@infradead.org>, <baolu.lu@linux.intel.com>,
        <agross@kernel.org>, <bjorn.andersson@linaro.org>,
        <konrad.dybcio@somainline.org>, <matthias.bgg@gmail.com>,
        <heiko@sntech.de>, <orsonzhai@gmail.com>,
        <baolin.wang@linux.alibaba.com>, <zhang.lyra@gmail.com>,
        <thierry.reding@gmail.com>, <jgg@nvidia.com>,
        <sricharan@codeaurora.org>, <yong.wu@mediatek.com>,
        <vdumpa@nvidia.com>, <jonathanh@nvidia.com>, <tglx@linutronix.de>,
        <shameerali.kolothum.thodi@huawei.com>,
        <thunder.leizhen@huawei.com>, <christophe.jaillet@wanadoo.fr>,
        <yangyingliang@huawei.com>, <jon@solid-run.com>,
        <iommu@lists.linux.dev>, <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-arm-msm@vger.kernel.org>,
        <linux-mediatek@lists.infradead.org>,
        <linux-rockchip@lists.infradead.org>,
        <linux-tegra@vger.kernel.org>,
        <virtualization@lists.linux-foundation.org>
Subject: Re: [PATCH 4/5] iommu: Regulate errno in ->attach_dev callback
 functions
Message-ID: <YyDkoIqWb8fy+vsi@Asurada-Nvidia>
References: <20220913082448.31120-1-nicolinc@nvidia.com>
 <20220913082448.31120-5-nicolinc@nvidia.com>
 <YyB3F/o3RfymqiFW@myrica>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <YyB3F/o3RfymqiFW@myrica>
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Sep 2022 20:14:28.7041
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 4703a67a-e720-4dfa-0d73-08da95c48ffc
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.235];Helo=[mail.nvidia.com]
X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT072.eop-nam11.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR12MB4260
X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,
        T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hi Jean,

On Tue, Sep 13, 2022 at 01:27:03PM +0100, Jean-Philippe Brucker wrote:
> External email: Use caution opening links or attachments
> 
> 
> Hi Nicolin,
> 
> On Tue, Sep 13, 2022 at 01:24:47AM -0700, Nicolin Chen wrote:
> > Following the new rules in include/linux/iommu.h kdocs, update all drivers
> > ->attach_dev callback functions to return ENODEV error code for all device
> > specific errors. It particularly excludes EINVAL from being used for such
> > error cases. For the same purpose, also replace one EINVAL with ENOMEM in
> > mtk_iommu driver.
> >
> > Note that the virtio-iommu does a viommu_domain_map_identity() call, which
> > returns either 0 or ENOMEM at this moment. Change to "return ret" directly
> > to allow it to pass an EINVAL in the future.
> [...]
> > diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> > index 80151176ba12..874c01634d2b 100644
> > --- a/drivers/iommu/virtio-iommu.c
> > +++ b/drivers/iommu/virtio-iommu.c
> > @@ -696,7 +696,7 @@ static int viommu_domain_finalise(struct viommu_endpoint *vdev,
> >               if (ret) {
> >                       ida_free(&viommu->domain_ids, vdomain->id);
> >                       vdomain->viommu = NULL;
> > -                     return -EOPNOTSUPP;
> > +                     return ret;
> 
> I think in the future it will be too easy to forget about the constrained
> return value of attach() while modifying some other part of the driver,
> and let an external helper return EINVAL. So I'd rather not propagate ret
> from outside of viommu_domain_attach() and finalise().
> 
> For the same reason I do prefer this solution over EMEDIUMTYPE, because
> it's too tempting to use exotic errno when they seem appropriate instead
> of boring ENODEV and EINVAL. The alternative would be adding a special
> purpose code to linux/errno.h, similarly to EPROBE_DEFER, but that might
> be excessive.
> 
> Since we can't guarantee that APIs like virtio or ida won't ever return
> EINVAL, we should set all return values:

Thanks for the inputs. Assuming your attached patch isn't officially
sent, I will group it into my next version.

Similarly, I will also double check other drivers, to make sure all
of them have explicit return values, other than "ret".