Re: [PULL 11/20] target/arm: Don't mishandle count when enabling or disabling PMU counters

[Thomas Huth <thuth@redhat.com>]

On 14/09/2022 13.52, Richard Henderson wrote:
> From: Peter Maydell <peter.maydell@linaro.org>
> 
> The PMU cycle and event counter infrastructure design requires that
> operations on the PMU register fields are wrapped in pmu_op_start()
> and pmu_op_finish() calls (or their more specific pmmcntr and
> pmevcntr equivalents).  This includes any changes to registers which
> affect whether the counter should be enabled or disabled, but we
> forgot to do this.
> 
> The effect of this bug is that in sequences like:
>   * disable the cycle counter (PMCCNTR) using the PMCNTEN register
>   * write a value such as 0xfffff000 to the PMCCNTR
>   * restart the counter by writing to PMCNTEN
> the value written to the cycle counter is corrupted, and it starts
> counting from the wrong place. (Essentially, we fail to record that
> the QEMU_CLOCK_VIRTUAL timestamp when the counter should be considered
> to have started counting is the point when PMCNTEN is written to enable
> the counter.)
> 
> Add the necessary bracketing calls, so that updates to the various
> registers which affect whether the PMU is counting are handled
> correctly.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Message-Id: <20220822132358.3524971-4-peter.maydell@linaro.org>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   target/arm/helper.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 45 insertions(+)

  Hi Peter, hi Richard,

this seems to break some Avocado based test(s) in our CI:

  make check-venv
  ./tests/venv/bin/avocado run tests/avocado/replay_kernel.py:ReplayKernelNormal.test_aarch64_virt

... fails with commit 01765386a88868ae993bcb but still passes
with the preceeding commit. Could you please have a look?

  Thanks,
   Thomas