From: Rob Herring <robh@kernel.org>
To: Will Deacon <will@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>,
Linux IOMMU <iommu@lists.linux-foundation.org>,
"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH] iommu: io-pgtable: Drop WARN for empty PTEs on unmap
Date: Thu, 11 Jul 2019 11:39:24 -0600 [thread overview]
Message-ID: <CAL_JsqJ6W-fFqNr9m1zQOdERjZ5v9EpVLTVyChevHKYFU4j4Jg@mail.gmail.com> (raw)
In-Reply-To: <20190711102303.pnvy4zlitusjjku7@willie-the-truck>
On Thu, Jul 11, 2019 at 4:23 AM Will Deacon <will@kernel.org> wrote:
>
> On Wed, Jul 10, 2019 at 04:31:19PM -0600, Rob Herring wrote:
> > If a region has been mapped sparsely (such as on page faults), the user
> > has to keep track of what was mapped or not in order to avoid warnings
> > when unmapping the entire region. Remove the WARN on empty PTEs to allow
> > unmapping sparsely mapped regions.
> >
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Robin Murphy <robin.murphy@arm.com>
> > Cc: Joerg Roedel <joro@8bytes.org>
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: iommu@lists.linux-foundation.org
> > Signed-off-by: Rob Herring <robh@kernel.org>
> > ---
> > This is needed for large (up to 1GB AIUI) scratch buffers on panfrost
> > which are mapped on demand on GPU page faults and can be unmapped on
> > memory pressure. Alternatively, I'd need to have a bitmap of mapped
> > pages to track what is mapped or not. Dropping the WARN seems like a
> > much simpler solution.
>
> I suppose an alternative would be to do an iova_to_phys() before you do the
> unmap(). Would that be acceptable?
Yeah, that should work. Not that efficient, but I don't think
releasing the memory is hot path.
Thanks,
Rob
> The WARN_ON() indicates invalid usage by
> the IOMMU API, so it would be a shame to lose it entirely and I'm hesitant
> to continue adding quirks at the rate we're currently doing so!
>
> Will
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prev parent reply other threads:[~2019-07-11 17:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-10 22:31 [RFC PATCH] iommu: io-pgtable: Drop WARN for empty PTEs on unmap Rob Herring
2019-07-11 10:23 ` Will Deacon
2019-07-11 17:39 ` Rob Herring [this message]
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