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Leo Yan 26bec96bc5 perf: arm_spe: Properly set hw.state on failures 
[ Upstream commit 283182c1c2 ]

When arm_spe_pmu_next_off() fails to calculate a valid limit, it returns
zero to indicate that tracing should not start.  However, the caller
arm_spe_perf_aux_output_begin() does not propagate this failure by
updating hwc->state, cause the error to be silently ignored by upper
layers.

Because hwc->state remains zero after a failure, arm_spe_pmu_start()
continues to programs filter registers unnecessarily.  The driver
still reports success to the perf core, so the core assumes the SPE
event was enabled and proceeds to enable other events.  This breaks
event group semantics: SPE is already stopped while other events in the
same group are enabled.

Fix this by updating arm_spe_perf_aux_output_begin() to return a status
code indicating success (0) or failure (-EIO).  Both the interrupt
handler and arm_spe_pmu_start() check the return value and call
arm_spe_pmu_stop() to set PERF_HES_STOPPED in hwc->state.

In the interrupt handler, the period (e.g., period_left) needs to be
updated, so PERF_EF_UPDATE is passed to arm_spe_pmu_stop().  When the
error occurs during event start, the trace unit is not yet enabled, so
a flag '0' is used to drain buffer and update state only.

Fixes: d5d9696b03 ("drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension")
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-03-04 07:19:31 -05:00
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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.