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Currently in system_call_exit() we have an optimisation where we disable MSR_RI (recoverable interrupt) and MSR_EE (external interrupt enable) in a single mtmsrd instruction. Unfortunately this will no longer work with THREAD_INFO_IN_TASK, because then the load of TI_FLAGS might fault and faulting with MSR_RI clear is treated as an unrecoverable exception which leads to a panic(). So change the code to only clear MSR_EE prior to loading TI_FLAGS, leaving the clear of MSR_RI until later. We have some latitude in where do the clear of MSR_RI. A bit of experimentation has shown that this location gives the least slow down. This still causes a noticeable slow down in our null_syscall performance. On a Power9 DD2.2: Before After Delta Delta % 955 cycles 999 cycles -44 -4.6% On the plus side this does simplify the code somewhat, because we don't have to reenable MSR_RI on the restore_math() or syscall_exit_work() paths which was necessitated previously by the optimisation. Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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.