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This reverts commit c44094eee3.
Although the semantics of the DMA API require only a clean operation
here, it turns out that the Qualcomm 'qcom_q6v5_mss' remoteproc driver
(ab)uses the DMA API for transferring the modem firmware to the secure
world via calls to Trustzone [1].
Once the firmware buffer has changed hands, _any_ access from the
non-secure side (i.e. Linux) will be detected on the bus and result in a
full system reset [2]. Although this is possible even with this revert
in place (due to speculative reads via the cacheable linear alias of
memory), anecdotally the problem occurs considerably more frequently
when the lines have not been invalidated, assumedly due to some
micro-architectural interactions with the cache hierarchy.
Revert the offending change for now, along with a comment, so that the
Qualcomm developers have time to fix the driver [3] to use a firmware
buffer which does not have a cacheable alias in the linear map.
Link: https://lore.kernel.org/r/20221114110329.68413-1-manivannan.sadhasivam@linaro.org [1]
Link: https://lore.kernel.org/r/CAMi1Hd3H2k1J8hJ6e-Miy5+nVDNzv6qQ3nN-9929B0GbHJkXEg@mail.gmail.com/ [2]
Link: https://lore.kernel.org/r/20221206092152.GD15486@thinkpad [2]
Reported-by: Amit Pundir <amit.pundir@linaro.org>
Reported-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Thorsten Leemhuis <regressions@leemhuis.info>
Cc: Sibi Sankar <quic_sibis@quicinc.com>
Signed-off-by: Will Deacon <will@kernel.org>
Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20221206103403.646-1-will@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
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Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text 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.