From: Arnd Bergmann <arnd@kernel.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Sven Peter <sven@svenpeter.dev>, Will Deacon <will@kernel.org>,
Joerg Roedel <joro@8bytes.org>, DTML <devicetree@vger.kernel.org>,
Hector Martin <marcan@marcan.st>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Marc Zyngier <maz@kernel.org>,
Mohamed Mediouni <mohamed.mediouni@caramail.com>,
Stan Skowronek <stan@corellium.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Mark Kettenis <mark.kettenis@xs4all.nl>,
"open list:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
Alexander Graf <graf@amazon.com>,
Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
Rob Herring <robh+dt@kernel.org>,
Rouven Czerwinski <r.czerwinski@pengutronix.de>
Subject: Re: [PATCH v4 0/3] Apple M1 DART IOMMU driver
Date: Wed, 14 Jul 2021 22:51:34 +0200 [thread overview]
Message-ID: <CAK8P3a18XK2mfMGbZ+M32Mbabhbkd+=DNrnzampOah_j=rWozw@mail.gmail.com> (raw)
In-Reply-To: <7261df01-34a9-4e53-37cd-ae1aa15b1fb4@arm.com>
On Wed, Jul 14, 2021 at 8:21 PM Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 2021-06-27 15:34, Sven Peter wrote:
> [...]
> > In the long term, I'd like to extend the dma-iommu framework itself to
> > support iommu pagesizes with a larger granule than the CPU pagesize if that is
> > something you agree with.
>
> BTW this isn't something we can fully support in general. IOMMU API
> users may expect this to work:
>
> iommu_map(domain, iova, page_to_phys(p1), PAGE_SIZE, prot);
> iommu_map(domain, iova + PAGE_SIZE, page_to_phys(p2), PAGE_SIZE, prot);
>
> Although they do in principle have visibility of pgsize_bitmap, I still
> doubt anyone is really prepared for CPU-page-aligned mappings to fail.
> Even at the DMA API level you could hide *some* of it (at the cost of
> effectively only having 1/4 of the usable address space), but there are
> still cases like where v4l2 has a hard requirement that a page-aligned
> scatterlist can be mapped into a contiguous region of DMA addresses.
I think that was the same conclusion we had earlier: the dma-mapping
interfaces should be possible for large iotlb pages, but any driver directly
using the IOMMU API, such as VFIO, would not work.
The question is how we can best allow one but not the other.
Arnd
next prev parent reply other threads:[~2021-07-14 20:51 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-27 14:34 [PATCH v4 0/3] Apple M1 DART IOMMU driver Sven Peter
2021-06-27 14:34 ` [PATCH v4 1/3] iommu: io-pgtable: add DART pagetable format Sven Peter
2021-06-28 10:54 ` Alexander Graf
2021-06-29 7:37 ` Sven Peter
2021-06-29 12:04 ` Alexander Graf
2021-06-30 13:53 ` Alyssa Rosenzweig
2021-07-13 19:17 ` Robin Murphy
2021-07-14 17:39 ` Sven Peter
2021-06-27 14:34 ` [PATCH v4 2/3] dt-bindings: iommu: add DART iommu bindings Sven Peter
2021-06-30 13:54 ` Alyssa Rosenzweig
2021-06-27 14:34 ` [PATCH v4 3/3] iommu: dart: Add DART iommu driver Sven Peter
2021-06-30 13:49 ` Alyssa Rosenzweig
2021-07-12 11:02 ` Sven Peter
2021-07-12 13:53 ` Alyssa Rosenzweig
2021-07-13 23:23 ` Robin Murphy
2021-07-15 16:41 ` Sven Peter
2021-07-19 18:15 ` Robin Murphy
2021-07-25 12:40 ` Sven Peter
2021-07-26 13:19 ` Alyssa Rosenzweig
2021-07-14 18:19 ` [PATCH v4 0/3] Apple M1 DART IOMMU driver Robin Murphy
2021-07-14 20:51 ` Arnd Bergmann [this message]
2021-07-15 6:52 ` Joerg Roedel
2021-07-16 6:24 ` Christoph Hellwig
2021-07-16 15:32 ` Robin Murphy
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