Peter Maydell <peter.mayd...@linaro.org> writes: > On 1 February 2017 at 15:05, Alex Bennée <alex.ben...@linaro.org> 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 <alex.ben...@linaro.org> >> Reviewed-by: Richard Henderson <r...@twiddle.net> > > 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).
Would it be enough to also queue the set_cpu_off work? The queue itself is safe to add to so you'll end up with a series of on/off deferred work that will eventually unwind itself when the CPU thread runs. > > thanks > -- PMM -- Alex Bennée
