From: Marek Szyprowski <m.szyprowski@samsung.com>
To: Vincent Whitchurch <vincent.whitchurch@axis.com>,
broonie@kernel.org, krzysztof.kozlowski@linaro.org,
andi@etezian.org, Christoph Hellwig <hch@lst.de>,
Robin Murphy <robin.murphy@arm.com>
Cc: kernel@axis.com, alim.akhtar@samsung.com,
linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-samsung-soc@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>
Subject: Re: [PATCH v2 2/4] spi: Fix cache corruption due to DMA/PIO overlap
Date: Fri, 30 Sep 2022 13:20:06 +0200 [thread overview]
Message-ID: <a4be6670-832a-ffac-4d68-e4a079eb2eed@samsung.com> (raw)
In-Reply-To: <20220927112117.77599-3-vincent.whitchurch@axis.com>
Hi,
CCed: Christoph and Robin, as the issue is partially dma-mapping related.
On 27.09.2022 13:21, Vincent Whitchurch wrote:
> The SPI core DMA mapping support performs cache management once for the
> entire message and not between transfers, and this leads to cache
> corruption if a message has two or more RX transfers with both
> transfers targeting the same cache line, and the controller driver
> decides to handle one using DMA and the other using PIO (for example,
> because one is much larger than the other).
>
> Fix it by syncing before/after the actual transfers. This also means
> that we can skip the sync during the map/unmap of the message.
>
> Fixes: 99adef310f68 ("spi: Provide core support for DMA mapping transfers")
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> ---
This patch landed in linux next-20220929 as commit 0c17ba73c08f ("spi:
Fix cache corruption due to DMA/PIO overlap"). Unfortunately it causes
kernel oops on one of my test systems:
8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 0000000c
[0000000c] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT SMP ARM
Modules linked in: cmac bnep btsdio hci_uart btbcm s5p_mfc btintel
brcmfmac bluetooth videobuf2_dma_contig videobuf2_memops videobuf2_v4l2
videobuf2_common videodev cfg80211 mc ecdh_generic ecc brcmutil
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted
6.0.0-rc7-next-20220929-dirty #12903
Hardware name: Samsung Exynos (Flattened Device Tree)
Workqueue: events ax88796c_work
PC is at dma_direct_sync_sg_for_device+0x24/0xb8
LR is at spi_transfer_one_message+0x4c4/0xabc
pc : [<c01cbcf0>] lr : [<c0739fcc>] psr: 20000013
...
Process kworker/0:1 (pid: 12, stack limit = 0xca429928)
Stack: (0xe0071d38 to 0xe0072000)
...
dma_direct_sync_sg_for_device from spi_transfer_one_message+0x4c4/0xabc
spi_transfer_one_message from __spi_pump_transfer_message+0x300/0x770
__spi_pump_transfer_message from __spi_sync+0x304/0x3f4
__spi_sync from spi_sync+0x28/0x40
spi_sync from axspi_read_rxq+0x98/0xc8
axspi_read_rxq from ax88796c_work+0x7a8/0xf6c
ax88796c_work from process_one_work+0x288/0x774
process_one_work from worker_thread+0x44/0x504
worker_thread from kthread+0xf0/0x124
kthread from ret_from_fork+0x14/0x2c
Exception stack(0xe0071fb0 to 0xe0071ff8)
...
---[ end trace 0000000000000000 ]---
This happens because sg_free_table() doesn't clear table->orig_nents nor
table->nents. If the given spi xfer object is reused without dma-mapped
buffer, then a NULL pointer de-reference happens at table->sgl
spi_dma_sync_for_device()/spi_dma_sync_for_cpu(). A possible fix would
be to zero table->orig_nents in spi_unmap_buf_attrs(). I will send a
patch for this soon.
However, I think that clearing table->orig_nents and table->nents should
be added to __sg_free_table() in lib/scatterlist.c to avoid this kind of
issue in the future. This however will be a significant change that
might break code somewhere, if it relies on the nents/orig_nents value
after calling sg_free_table(). Christoph, Robin - what is your opinion?
> drivers/spi/spi.c | 109 +++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 88 insertions(+), 21 deletions(-)
>
> ...
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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next prev parent reply other threads:[~2022-09-30 11:21 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-27 11:21 [PATCH v2 0/4] spi: Fix DMA bugs in (not only) spi-s3c64xx Vincent Whitchurch
2022-09-27 11:21 ` [PATCH v2 1/4] spi: Save current RX and TX DMA devices Vincent Whitchurch
2022-09-27 11:21 ` [PATCH v2 2/4] spi: Fix cache corruption due to DMA/PIO overlap Vincent Whitchurch
2022-09-30 11:20 ` Marek Szyprowski [this message]
2022-09-30 12:10 ` Robin Murphy
2022-10-03 11:29 ` Vincent Whitchurch
2022-09-27 11:21 ` [PATCH v2 3/4] spi: Split transfers larger than max size Vincent Whitchurch
2023-06-22 19:48 ` Eddie James
2023-06-22 21:16 ` Mark Brown
2023-06-23 16:45 ` Eddie James
2023-06-23 17:16 ` Mark Brown
2022-09-27 11:21 ` [PATCH v2 4/4] spi: s3c64xx: Fix large transfers with DMA Vincent Whitchurch
2022-09-28 17:27 ` [PATCH v2 0/4] spi: Fix DMA bugs in (not only) spi-s3c64xx Mark Brown
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