linux-kernel - Re: [PATCH v2 06/11] iommufd: IOMMU_HWPT

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Message-ID: <ZGfPME8zrxfJ+f8E@Asurada-Nvidia>
Date:   Fri, 19 May 2023 12:34:08 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     "Liu, Jingqi" <jingqi.liu@...el.com>
CC:     Yi Liu <yi.l.liu@...el.com>, <joro@...tes.org>,
        <alex.williamson@...hat.com>, <jgg@...dia.com>,
        <kevin.tian@...el.com>, <robin.murphy@....com>,
        <baolu.lu@...ux.intel.com>, <cohuck@...hat.com>,
        <eric.auger@...hat.com>, <kvm@...r.kernel.org>,
        <mjrosato@...ux.ibm.com>, <chao.p.peng@...ux.intel.com>,
        <yi.y.sun@...ux.intel.com>, <peterx@...hat.com>,
        <jasowang@...hat.com>, <shameerali.kolothum.thodi@...wei.com>,
        <lulu@...hat.com>, <suravee.suthikulpanit@....com>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <zhenzhong.duan@...el.com>
Subject: Re: [PATCH v2 06/11] iommufd: IOMMU_HWPT_ALLOC allocation with user
 data

On Wed, May 17, 2023 at 11:08:12AM +0800, Liu, Jingqi wrote:

> > +     /*
> > +      * All drivers support IOMMU_HWPT_TYPE_DEFAULT, so pass it through.
> > +      * For any other hwpt_type, check the ops->domain_alloc_user_data_len
> > +      * presence and its result.
> > +      */
> > +     if (cmd->hwpt_type != IOMMU_HWPT_TYPE_DEFAULT) {
> > +             if (!ops->domain_alloc_user_data_len) {
> > +                     rc = -EOPNOTSUPP;
> > +                     goto out_put_idev;
> > +             }
> > +             klen = ops->domain_alloc_user_data_len(cmd->hwpt_type);
> > +             if (WARN_ON(klen < 0)) {
> > +                     rc = -EINVAL;
> > +                     goto out_put_pt;
> > +             }
> Would it be better if the later check "klen" is moved here ?
>     if (klen) {
>                 [...]
>     }
> If this check fails here, there's no need to execute the code after it.
> If this path is not executed, "klen" is 0, and there's no need to check it.
> Do I understand it right ?

Makes sense. And the klen value isn't really being used. So,
we may likely change it to a bool one. Also, I'm thinking of
forcing a !!cmd->data_len for a non-DEFAULT hwpt_type:

+	if (cmd->hwpt_type != IOMMU_HWPT_TYPE_DEFAULT) {
+		if (!cmd->data_len) {
+			rc = -EINVAL;
+			goto out_put_pt;
+		}
+		if (!ops->domain_alloc_user_data_len) {
+			rc = -EOPNOTSUPP;
+			goto out_put_pt;
+		}
+		if (!ops->hwpt_type_is_supported(cmd->hwpt_type)) {
+			rc = -EINVAL;
+			goto out_put_pt;
+		}

Then, for the latter part, simply:
+	if (cmd->data_len) {
+		// malloc data
+	}

Thanks
Nic