mirror of https://github.com/xemu-project/xemu.git
74112400df
In case of programmable counters configured to count inst/cycles we often end-up with counter not incrementing at all from kernel's perspective. For example: - Kernel configures hpm3 to count instructions and sets hpmcounter to -10000 and all modes except U mode are inhibited. - In QEMU we configure a timer to expire after ~10000 instructions. - Problem is, it's often the case that kernel might not even schedule Umode task and we hit the timer callback in QEMU. - In the timer callback we inject the interrupt into kernel, kernel runs the handler and reads hpmcounter3 value. - Given QEMU maintains individual counters to count for each privilege mode, and given umode never ran, the umode counter didn't increment and QEMU returns same value as was programmed by the kernel when starting the counter. - Kernel checks for overflow using previous and current value of the counter and reprograms the counter given there wasn't an overflow as per the counter value. (Which itself is a problem. We have QEMU telling kernel that counter3 overflowed but the counter value returned by QEMU doesn't seem to reflect that.). This change makes sure that timer is reprogrammed from the handler if the counter didn't overflow based on the counter value. Second, this change makes sure that whenever the counter is read, it's value is updated to reflect the latest count. Signed-off-by: Rajnesh Kanwal <rkanwal@rivosinc.com> Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com> Message-ID: <20240711-smcntrpmf_v7-v8-11-b7c38ae7b263@rivosinc.com> Signed-off-by: Alistair Francis <alistair.francis@wdc.com> |
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