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A disassembly of interrupt_exit_kernel_prepare() shows a useless read of MD_AP register. This is shown by r9 being re-used immediately without doing anything with the value read. c000e0e0: 60 00 00 00 nop c000e0e4: ===> 7d 3a c2 a6 mfmd_ap r9 <==== c000e0e8: 7d 20 00 a6 mfmsr r9 c000e0ec: 7c 51 13 a6 mtspr 81,r2 c000e0f0: 81 3f 00 84 lwz r9,132(r31) c000e0f4: 71 29 80 00 andi. r9,r9,32768 kuap_get_and_assert_locked() is paired with kuap_kernel_restore() and are only used in interrupt_exit_kernel_prepare(). The value returned by kuap_get_and_assert_locked() is only used by kuap_kernel_restore(). On 8xx, kuap_kernel_restore() doesn't use the value read by kuap_get_and_assert_locked() so modify kuap_get_and_assert_locked() to not perform the read of MD_AP and return 0 instead. The same applies on BOOKE. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/bcbc84c2dd90bb1021da792b1968cdc22112dad8.1689091022.git.christophe.leroy@csgroup.eu
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 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.