From: Robin Murphy <robin.murphy@arm.com>
To: Jani Nikula <jani.nikula@linux.intel.com>,
Tom Murphy <murphyt7@tcd.ie>,
iommu@lists.linux-foundation.org
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
Rodrigo Vivi <rodrigo.vivi@intel.com>,
David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Kukjin Kim <kgene@kernel.org>,
Krzysztof Kozlowski <krzk@kernel.org>,
David Woodhouse <dwmw2@infradead.org>,
Lu Baolu <baolu.lu@linux.intel.com>,
Andy Gross <agross@kernel.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Matthias Brugger <matthias.bgg@gmail.com>,
Rob Clark <robdclark@gmail.com>, Heiko Stuebner <heiko@sntech.de>,
Gerald Schaefer <gerald.schaefer@de.ibm.com>,
Thierry Reding <thierry.reding@gmail.com>,
Jonathan Hunter <jonathanh@nvidia.com>,
Jean-Philippe Brucker <jean-philippe@linaro.org>,
Alex Williamson <alex.williamson@redhat.com>,
Cornelia Huck <cohuck@redhat.com>,
Julien Grall <julien.grall@arm.com>,
Marc Zyngier <maz@kernel.org>, Eric Auger <eric.auger@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-samsung-soc@vger.kernel.org, linux-arm-msm@vger.kernel.org,
linux-mediatek@lists.infradead.org,
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linux-tegra@vger.kernel.org,
virtualization@lists.linux-foundation.org, kvm@vger.kernel.org
Subject: Re: [PATCH 0/8] Convert the intel iommu driver to the dma-iommu api
Date: Mon, 23 Dec 2019 11:29:17 +0000 [thread overview]
Message-ID: <432d306c-fe9f-75b2-f0f7-27698f1467ad@arm.com> (raw)
In-Reply-To: <87blrzwcn8.fsf@intel.com>
On 2019-12-23 10:37 am, Jani Nikula wrote:
> On Sat, 21 Dec 2019, Tom Murphy <murphyt7@tcd.ie> wrote:
>> This patchset converts the intel iommu driver to the dma-iommu api.
>>
>> While converting the driver I exposed a bug in the intel i915 driver
>> which causes a huge amount of artifacts on the screen of my
>> laptop. You can see a picture of it here:
>> https://github.com/pippy360/kernelPatches/blob/master/IMG_20191219_225922.jpg
>>
>> This issue is most likely in the i915 driver and is most likely caused
>> by the driver not respecting the return value of the
>> dma_map_ops::map_sg function. You can see the driver ignoring the
>> return value here:
>> https://github.com/torvalds/linux/blob/7e0165b2f1a912a06e381e91f0f4e495f4ac3736/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c#L51
>>
>> Previously this didn’t cause issues because the intel map_sg always
>> returned the same number of elements as the input scatter gather list
>> but with the change to this dma-iommu api this is no longer the
>> case. I wasn’t able to track the bug down to a specific line of code
>> unfortunately.
>>
>> Could someone from the intel team look at this?
>
> Let me get this straight. There is current API that on success always
> returns the same number of elements as the input scatter gather
> list. You propose to change the API so that this is no longer the case?
No, the API for dma_map_sg() has always been that it may return fewer
DMA segments than nents - see Documentation/DMA-API.txt (and otherwise,
the return value would surely be a simple success/fail condition).
Relying on a particular implementation behaviour has never been strictly
correct, even if it does happen to be a very common behaviour.
> A quick check of various dma_map_sg() calls in the kernel seems to
> indicate checking for 0 for errors and then ignoring the non-zero return
> is a common pattern. Are you sure it's okay to make the change you're
> proposing?
Various code uses tricks like just iterating the mapped list until the
first segment with zero sg_dma_len(). Others may well simply have bugs.
Robin.
> Anyway, due to the time of year and all, I'd like to ask you to file a
> bug against i915 at [1] so this is not forgotten, and please let's not
> merge the changes before this is resolved.
>
>
> Thanks,
> Jani.
>
>
> [1] https://gitlab.freedesktop.org/drm/intel/issues/new
>
>
next prev parent reply other threads:[~2019-12-23 11:29 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-21 15:03 [PATCH 0/8] Convert the intel iommu driver to the dma-iommu api Tom Murphy
2019-12-21 15:03 ` [PATCH 1/8] iommu/vt-d: clean up 32bit si_domain assignment Tom Murphy
2019-12-21 23:46 ` Arvind Sankar
2019-12-23 3:00 ` Lu Baolu
2019-12-21 15:03 ` [PATCH 2/8] iommu/vt-d: Use default dma_direct_* mapping functions for direct mapped devices Tom Murphy
2019-12-21 15:03 ` [PATCH 3/8] iommu/vt-d: Remove IOVA handling code from non-dma_ops path Tom Murphy
2020-03-20 6:30 ` Tom Murphy
2020-03-20 7:06 ` Lu Baolu
2019-12-21 15:03 ` [PATCH 4/8] iommu: Handle freelists when using deferred flushing in iommu drivers Tom Murphy
2019-12-21 15:03 ` [PATCH 5/8] iommu: Add iommu_dma_free_cpu_cached_iovas function Tom Murphy
2019-12-21 15:03 ` [PATCH 6/8] iommu: allow the dma-iommu api to use bounce buffers Tom Murphy
2019-12-24 10:20 ` kbuild test robot
2019-12-21 15:03 ` [PATCH 7/8] iommu/vt-d: Convert intel iommu driver to the iommu ops Tom Murphy
2019-12-21 15:04 ` [PATCH 8/8] DO NOT MERGE: iommu: disable list appending in dma-iommu Tom Murphy
2019-12-23 10:37 ` [PATCH 0/8] Convert the intel iommu driver to the dma-iommu api Jani Nikula
2019-12-23 11:29 ` Robin Murphy [this message]
2019-12-23 11:41 ` Jani Nikula
2020-03-20 6:28 ` Tom Murphy
2020-05-29 0:00 ` Logan Gunthorpe
2020-05-29 12:45 ` Christoph Hellwig
2020-05-29 19:05 ` Logan Gunthorpe
2020-05-29 21:11 ` Marek Szyprowski
2020-05-29 21:21 ` Logan Gunthorpe
2020-08-24 0:04 ` Tom Murphy
2020-08-26 18:26 ` Alex Deucher
2020-08-27 21:36 ` Logan Gunthorpe
2020-08-27 23:34 ` Tom Murphy
2020-09-03 20:26 ` Tom Murphy
2020-09-08 15:28 ` [Intel-gfx] " Tvrtko Ursulin
2020-09-08 15:44 ` Logan Gunthorpe
[not found] ` <b27cae1f-07ff-bef2-f125-a5f0d968016d@linux.intel.com>
2020-09-08 22:43 ` Tom Murphy
2020-09-09 9:16 ` Tvrtko Ursulin
[not found] ` <ea24e077-5aa6-dd8e-69a7-d186b606703f@linux.intel.com>
2020-09-10 13:33 ` Tom Murphy
2020-09-10 13:34 ` Tom Murphy
2020-08-26 18:14 ` Robin Murphy
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