linux-kernel - Re: [PATCH v7 4/5] iommu: Use EINVAL for incompatible device/domain in ->attach

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Message-ID: <Y2mfaG1/6hd1qykW@Asurada-Nvidia>
Date:   Mon, 7 Nov 2022 16:14:32 -0800
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Will Deacon <will@...nel.org>
CC:     <joro@...tes.org>, <robin.murphy@....com>, <jgg@...dia.com>,
        <kevin.tian@...el.com>, <quic_jjohnson@...cinc.com>,
        <suravee.suthikulpanit@....com>, <robdclark@...il.com>,
        <dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>,
        <yong.wu@...iatek.com>, <matthias.bgg@...il.com>,
        <orsonzhai@...il.com>, <baolin.wang@...ux.alibaba.com>,
        <zhang.lyra@...il.com>, <thierry.reding@...il.com>,
        <vdumpa@...dia.com>, <jonathanh@...dia.com>,
        <jean-philippe@...aro.org>, <tglx@...utronix.de>,
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        <yangyingliang@...wei.com>, <quic_saipraka@...cinc.com>,
        <jon@...id-run.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 v7 4/5] iommu: Use EINVAL for incompatible device/domain
 in ->attach_dev

On Mon, Nov 07, 2022 at 03:26:45PM +0000, Will Deacon wrote:

> > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > index ba47c73f5b8c..01fd7df16cb9 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> > @@ -2430,23 +2430,14 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> >                       goto out_unlock;
> >               }
> >       } else if (smmu_domain->smmu != smmu) {
> > -             dev_err(dev,
> > -                     "cannot attach to SMMU %s (upstream of %s)\n",
> > -                     dev_name(smmu_domain->smmu->dev),
> > -                     dev_name(smmu->dev));
> > -             ret = -ENXIO;
> > +             ret = -EINVAL;
> >               goto out_unlock;
> >       } else if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1 &&
> >                  master->ssid_bits != smmu_domain->s1_cfg.s1cdmax) {
> > -             dev_err(dev,
> > -                     "cannot attach to incompatible domain (%u SSID bits != %u)\n",
> > -                     smmu_domain->s1_cfg.s1cdmax, master->ssid_bits);
> >               ret = -EINVAL;
> >               goto out_unlock;
> >       } else if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1 &&
> >                  smmu_domain->stall_enabled != master->stall_enabled) {
> > -             dev_err(dev, "cannot attach to stall-%s domain\n",
> > -                     smmu_domain->stall_enabled ? "enabled" : "disabled");
> >               ret = -EINVAL;
> >               goto out_unlock;
> >       }

> I think it would be helpful to preserve these messages using
> dev_err_ratelimited() so that attach failure can be diagnosed without
> having to hack the messages back into the driver.

Thank you for the review.

The change is already picked up last week. Yet, I can add prints
back with a followup patch, if no one has a problem with that.

Also, I am not quite sure what the use case would be to have an
error print. Perhaps dev_dbg() would be more fitting if it is
just for diagnosis?

Thanks
Nic