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In case the non-paged data of a SKB carries protocol header and protocol
payload to be transmitted on a certain platform that the DMA AXI address
width is configured to 40-bit/48-bit, or the size of the non-paged data
is bigger than TSO_MAX_BUFF_SIZE on a certain platform that the DMA AXI
address width is configured to 32-bit, then this SKB requires at least
two DMA transmit descriptors to serve it.
For example, three descriptors are allocated to split one DMA buffer
mapped from one piece of non-paged data:
dma_desc[N + 0],
dma_desc[N + 1],
dma_desc[N + 2].
Then three elements of tx_q->tx_skbuff_dma[] will be allocated to hold
extra information to be reused in stmmac_tx_clean():
tx_q->tx_skbuff_dma[N + 0],
tx_q->tx_skbuff_dma[N + 1],
tx_q->tx_skbuff_dma[N + 2].
Now we focus on tx_q->tx_skbuff_dma[entry].buf, which is the DMA buffer
address returned by DMA mapping call. stmmac_tx_clean() will try to
unmap the DMA buffer _ONLY_IF_ tx_q->tx_skbuff_dma[entry].buf
is a valid buffer address.
The expected behavior that saves DMA buffer address of this non-paged
data to tx_q->tx_skbuff_dma[entry].buf is:
tx_q->tx_skbuff_dma[N + 0].buf = NULL;
tx_q->tx_skbuff_dma[N + 1].buf = NULL;
tx_q->tx_skbuff_dma[N + 2].buf = dma_map_single();
Unfortunately, the current code misbehaves like this:
tx_q->tx_skbuff_dma[N + 0].buf = dma_map_single();
tx_q->tx_skbuff_dma[N + 1].buf = NULL;
tx_q->tx_skbuff_dma[N + 2].buf = NULL;
On the stmmac_tx_clean() side, when dma_desc[N + 0] is closed by the
DMA engine, tx_q->tx_skbuff_dma[N + 0].buf is a valid buffer address
obviously, then the DMA buffer will be unmapped immediately.
There may be a rare case that the DMA engine does not finish the
pending dma_desc[N + 1], dma_desc[N + 2] yet. Now things will go
horribly wrong, DMA is going to access a unmapped/unreferenced memory
region, corrupted data will be transmited or iommu fault will be
triggered :(
In contrast, the for-loop that maps SKB fragments behaves perfectly
as expected, and that is how the driver should do for both non-paged
data and paged frags actually.
This patch corrects DMA map/unmap sequences by fixing the array index
for tx_q->tx_skbuff_dma[entry].buf when assigning DMA buffer address.
Tested and verified on DWXGMAC CORE 3.20a
Reported-by: Suraj Jaiswal <quic_jsuraj@quicinc.com>
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.