linux-kernel - Re: [PATCH v2 10/22] iommufd/viommmu: Add IOMMUFD_CMD_VCMDQ

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Message-ID: <aA/P02wgX27/EjBS@Asurada-Nvidia>
Date: Mon, 28 Apr 2025 11:58:27 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
CC: <jgg@...dia.com>, <kevin.tian@...el.com>, <corbet@....net>,
	<will@...nel.org>, <bagasdotme@...il.com>, <robin.murphy@....com>,
	<joro@...tes.org>, <thierry.reding@...il.com>, <vdumpa@...dia.com>,
	<jonathanh@...dia.com>, <shuah@...nel.org>, <jsnitsel@...hat.com>,
	<nathan@...nel.org>, <peterz@...radead.org>, <yi.l.liu@...el.com>,
	<mshavit@...gle.com>, <praan@...gle.com>, <zhangzekun11@...wei.com>,
	<iommu@...ts.linux.dev>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-tegra@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
	<patches@...ts.linux.dev>, <mochs@...dia.com>, <alok.a.tiwari@...cle.com>,
	<vasant.hegde@....com>
Subject: Re: [PATCH v2 10/22] iommufd/viommmu: Add IOMMUFD_CMD_VCMDQ_ALLOC
 ioctl

On Mon, Apr 28, 2025 at 09:32:04AM +0800, Baolu Lu wrote:
> On 4/26/25 13:58, Nicolin Chen wrote:
> > +int iommufd_vcmdq_alloc_ioctl(struct iommufd_ucmd *ucmd)
> > +{
> > +	struct iommu_vcmdq_alloc *cmd = ucmd->cmd;
> > +	struct iommufd_viommu *viommu;
> > +	struct iommufd_vcmdq *vcmdq;
> > +	struct page **pages;
> > +	int max_npages, i;
> > +	dma_addr_t end;
> > +	int rc;
> > +
> > +	if (cmd->flags || cmd->type == IOMMU_VCMDQ_TYPE_DEFAULT)
> 
> I don't follow the check of 'cmd->type == IOMMU_VCMDQ_TYPE_DEFAULT'
> here. My understanding is that it states that "other values of type are
> not supported". If so, shouldn't it be,
> 
> 	if (cmd->flags || cmd->type != IOMMU_VCMDQ_TYPE_DEFAULT)
> 
> ?

No. Only other (new) types will be supported. We have this:
"* @IOMMU_VCMDQ_TYPE_DEFAULT: Reserved for future use"
which means driver should define a new type.

We have the same DEFAULT type in vIOMMU/vEVENTQ allocators by
the way.

Thanks
Nicolin