linux-kernel - Re: [PATCH v5 08/14] iommufd/viommu: Add iommufd_viommu_report

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Message-ID: <20250110145149.GH5556@nvidia.com>
Date: Fri, 10 Jan 2025 10:51:49 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, "corbet@....net" <corbet@....net>,
	"will@...nel.org" <will@...nel.org>,
	"joro@...tes.org" <joro@...tes.org>,
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	"robin.murphy@....com" <robin.murphy@....com>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
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	"shuah@...nel.org" <shuah@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
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	"ddutile@...hat.com" <ddutile@...hat.com>,
	"Liu, Yi L" <yi.l.liu@...el.com>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: Re: [PATCH v5 08/14] iommufd/viommu: Add iommufd_viommu_report_event
 helper

On Fri, Jan 10, 2025 at 07:12:46AM +0000, Tian, Kevin wrote:

> > +	if (!viommu)
> > +		return -ENODEV;
> > +	if (WARN_ON_ONCE(!viommu->ops || !viommu->ops-
> > >supports_veventq ||
> > +			 !viommu->ops->supports_veventq(type)))
> > +		return -EOPNOTSUPP;
> 
> Hmm the driver knows which type is supported by itself before
> calling this helper. Why bother having the helper calling into
> the driver again to verify?

Indeed, it might make sense to protect this with

        if (IS_ENABLED(CONFIG_IOMMUFD_TEST))

As a compiled out assertion

Or drop it

We shouldn't have unnecessary argument validation on fast paths,
!viommu should go too.

Jason