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

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Date:   Tue, 21 Jun 2022 13:59:55 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        "Tian, Kevin" <kevin.tian@...el.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 Mon, Jun 20, 2022 at 01:03:17AM -0300, Jason Gunthorpe wrote:
> 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.

OK. I will keep it simple then. If Kevin or other has a further
objection, please let us know.

Thanks
Nic