linux-kernel - Re: [PATCH v6 10/25] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE

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Message-ID: <aE+976F9zPsjtfry@nvidia.com>
Date: Sun, 15 Jun 2025 23:47:11 -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>, <dwmw2@...radead.org>
Subject: Re: [PATCH v6 10/25] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC
 ioctl

On Mon, Jun 16, 2025 at 02:12:04PM +0800, Baolu Lu wrote:
> On 6/14/25 15:14, Nicolin Chen wrote:
> > +	if (!viommu->ops || !viommu->ops->get_hw_queue_size ||
> > +	    !viommu->ops->hw_queue_init_phys) {
> > +		rc = -EOPNOTSUPP;
> > +		goto out_put_viommu;
> > +	}

Hmm, here it does abort when !viommu->ops->hw_queue_init_phys ..

> > +	/*
> > +	 * FIXME once ops->hw_queue_init is introduced, this should check "if
> > +	 * ops->hw_queue_init_phys". And "access" should be initialized to NULL.
> > +	 */
> 
> I just don't follow here. Up until now, only viommu->ops->
> hw_queue_init_phys has been added, which means the current code only
> supports hardware queues that access guest memory using physical
> addresses. The access object is not needed for the other type of
> hardware queue that uses guest IOVA.
> 
> So, why not just abort here if ops->hw_queue_init_phys is not supported
> by the IOMMU driver?

.. so, it already does.

> Leave other logics to the patches that introduce
> ops->hw_queue_init? I guess that would make this patch more readible.

The patch is doing in the way to support the hw_queue_init_phys
case only. It is just adding some extra FIXMEs as the guideline
for the future patch adding hw_queue_init op.

I personally don't feel these are confusing. Maybe you can help
point out what specific wording feels odd here? Maybe "FIXME"s
should be "TODO"s?

I could also drop all of these guideline if they are considered
very unnecessary.

Thanks
Nicolin