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

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Message-ID: <Z4Fpt9ftiZByVEpO@Asurada-Nvidia>
Date: Fri, 10 Jan 2025 10:40:55 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: "Tian, Kevin" <kevin.tian@...el.com>, "corbet@....net" <corbet@....net>,
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	<linux-kernel@...r.kernel.org>, "iommu@...ts.linux.dev"
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	<smostafa@...gle.com>, "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 10:51:49AM -0400, Jason Gunthorpe wrote:
> 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.

Ack. I will drop those two if-statments.

Nicolin