linux-kernel - Re: [PATCH v6 05/14] iommufd: Add IOMMUFD_OBJ_VEVENTQ and IOMMUFD_CMD_VEVENTQ

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Message-ID: <20250218180805.GI4099685@nvidia.com>
Date: Tue, 18 Feb 2025 14:08:05 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, corbet@....net, will@...nel.org, joro@...tes.org,
	suravee.suthikulpanit@....com, robin.murphy@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com, shuah@...nel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
	eric.auger@...hat.com, jean-philippe@...aro.org, mdf@...nel.org,
	mshavit@...gle.com, shameerali.kolothum.thodi@...wei.com,
	smostafa@...gle.com, ddutile@...hat.com, yi.l.liu@...el.com,
	patches@...ts.linux.dev
Subject: Re: [PATCH v6 05/14] iommufd: Add IOMMUFD_OBJ_VEVENTQ and
 IOMMUFD_CMD_VEVENTQ_ALLOC

On Tue, Feb 18, 2025 at 09:47:50AM -0800, Nicolin Chen wrote:
> I think we can do:
> 	if (!list_empty(list)) {
> 		struct iommufd_vevent *next;
> 
> 		next = list_first_entry(list, struct iommufd_vevent, node);
> 		if (next == &veventq->overflow) {
> 			/* Make a copy of the overflow node for copy_to_user */
> 			vevent = kzalloc(sizeof(*vevent), GFP_ATOMIC);
> 			if (!vevent)
> 				goto out_unlock;
> 		}
> 		list_del(&next->node);
> 		if (vevent)
> 			memcpy(vevent, next, sizeof(*vevent));
> 		else
> 			vevent = next;
> 	}

That looks right

> > > +int iommufd_veventq_alloc(struct iommufd_ucmd *ucmd)
> > > +{
> > > +	struct iommu_veventq_alloc *cmd = ucmd->cmd;
> > > +	struct iommufd_veventq *veventq;
> > > +	struct iommufd_viommu *viommu;
> > > +	int fdno;
> > > +	int rc;
> > > +
> > > +	if (cmd->flags || cmd->type == IOMMU_VEVENTQ_TYPE_DEFAULT)
> > > +		return -EOPNOTSUPP;
> > > +	if (!cmd->veventq_depth)
> > > +		return -EINVAL;
> > 
> > Check __reserved for 0 too
> 
> Kevin is suggesting a 32-bit flag field, so I think we can drop
> the __reserved in that case.

Those are different structs?

Jason