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The icache will be flushed in switch_to() if force_icache_flush is true,
or in flush_icache_deferred() if icache_stale_mask is set. Between
setting force_icache_flush to false and calculating the new
icache_stale_mask, preemption needs to be disabled. There are two
reasons for this:
1. If CPU migration happens between force_icache_flush = false, and the
icache_stale_mask is set, an icache flush will not be emitted.
2. smp_processor_id() is used in set_icache_stale_mask() to mark the
current CPU as not needing another flush since a flush will have
happened either by userspace or by the kernel when performing the
migration. smp_processor_id() is currently called twice with preemption
enabled which causes a race condition. It allows
icache_stale_mask to be populated with inconsistent CPU ids.
Resolve these two issues by setting the icache_stale_mask before setting
force_icache_flush to false, and using get_cpu()/put_cpu() to obtain the
smp_processor_id().
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Fixes: 6b9391b581 ("riscv: Include riscv_set_icache_flush_ctx prctl")
Link: https://lore.kernel.org/r/20240903-fix_fencei_optimization-v2-1-8025f20171fc@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
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.