linux-kernel - Re: [PATCH v2 08/22] iommufd: Abstract iopt_pin_pages and iopt_unpin

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Message-ID: <aBEUYdlCLcH70UlT@google.com>
Date: Tue, 29 Apr 2025 18:03:13 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, corbet@....net, will@...nel.org,
	bagasdotme@...il.com, robin.murphy@....com, joro@...tes.org,
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	shuah@...nel.org, jsnitsel@...hat.com, nathan@...nel.org,
	peterz@...radead.org, yi.l.liu@...el.com, mshavit@...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
Subject: Re: [PATCH v2 08/22] iommufd: Abstract iopt_pin_pages and
 iopt_unpin_pages helpers

On Mon, Apr 28, 2025 at 04:34:14PM -0700, Nicolin Chen wrote:
> On Mon, Apr 28, 2025 at 03:12:33PM -0700, Nicolin Chen wrote:
> > On Mon, Apr 28, 2025 at 08:14:19PM +0000, Pranjal Shrivastava wrote:
> > > On Fri, Apr 25, 2025 at 10:58:03PM -0700, Nicolin Chen wrote:
> > > > +	iopt_for_each_contig_area(&iter, area, iopt, iova, last_iova) {
> > > > +		unsigned long last = min(last_iova, iopt_area_last_iova(area));
> > > > +		unsigned long last_index = iopt_area_iova_to_index(area, last);
> > > > +		unsigned long index =
> > > > +			iopt_area_iova_to_index(area, iter.cur_iova);
> > > > +
> > > > +		if (area->prevent_access ||
> > > 
> > > Nit:
> > > Shouldn't we return -EBUSY or something if (area->prevent_access == 1) ?
> > > IIUC, this just means that an unmap attempt is in progress, hence avoid
> > > accessing the area.
> > 
> > Maybe. But this is what it was. So we need a different patch to
> > change that.
> 
> Rereading the code. The prevent_access is set by an unmap(), which
> means there shouldn't be any pin() and rw() as the caller should
> finish unmap() first.
> 
> In the newer use case of vCMDQ, it's similar. If VMM is unmapping
> the stage-2 mapping, it shouldn't try to allocate a vCMDQ.
> 
> -EBUSY makes some sense, but -EINVAL could still stand.
> 
> So, I am leaving it as is, since this patch is just about moving
> the functions for sharing.

Ack. I don't have a strong preference too. This should be fine, we can
re-visit this if needed in the future.

Reviewed-by: Pranjal Shrivastava <praan@...gle.com>

> 
> Nicolin

Thanks!