linux-kernel - Re: [PATCH v2 5/5] vfio/iommu_type1: Simplify group attachment

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Message-ID: <20220620040317.GD5219@nvidia.com>
Date:   Mon, 20 Jun 2022 01:03:17 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     "robin.murphy@....com" <robin.murphy@....com>,
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Subject: Re: [PATCH v2 5/5] vfio/iommu_type1: Simplify group attachment

On Fri, Jun 17, 2022 at 04:07:20PM -0700, Nicolin Chen wrote:

> > > > > +     vfio_iommu_aper_expand(iommu, &iova_copy);
> > > >
> > > > but now it's done for every group detach. The aperture is decided
> > > > by domain geometry which is not affected by attached groups.
> > >
> > > Yea, I've noticed this part. Actually Jason did this change for
> > > simplicity, and I think it'd be safe to do so?
> > 
> > Perhaps detach_destroy() can return a Boolean to indicate whether
> > a domain is destroyed.
> 
> It could be a solution but doesn't feel that common for a clean
> function to have a return value indicating a special case. Maybe
> passing in "&domain" so that we can check if it's NULL after?

It is harmless to do every time, it just burns a few CPU cycles on a
slow path. We don't need complexity to optmize it.

Jason