Re: [Qemu-arm] [PATCH v9 20/25] target-arm/powerctl: defer cpu reset work to CPU context

[Peter Maydell]

On 1 February 2017 at 15:05, Alex Bennée <address@hidden> wrote:
> When switching a new vCPU on we want to complete a bunch of the setup
> work before we start scheduling the vCPU thread. To do this cleanly we
> defer vCPU setup to async work which will run the vCPUs execution
> context as the thread is woken up. The scheduling of the work will kick
> the vCPU awake.
>
> This avoids potential races in MTTCG system emulation.
>
> Signed-off-by: Alex Bennée <address@hidden>
> Reviewed-by: Richard Henderson <address@hidden>

Can we now have races between arm_set_cpu_on() and
arm_set_cpu_off() ? It's not clear to me what prevents that.

With this change our PSCI CPU_ON is no longer effectively
atomic, which means we need to think about the races
between PSCI CPU_ON and CPU_OFF, and the fact that the
core might be in what the PSCI spec section 6.6
calls an ON_PENDING state (ie CPU_ON has been called
for it but it hasn't actually booted yet).

thanks
-- PMM