On Tue, Nov 22, 2022 at 04:06:25PM +0100, Thomas Gleixner wrote: > On Tue, Nov 22 2022 at 10:20, Peter Zijlstra wrote: > > > On Mon, Nov 21, 2022 at 01:26:28PM +1300, Kai Huang wrote: > > > >> Shutting down the TDX module requires calling TDH.SYS.LP.SHUTDOWN on all > >> BIOS-enabled CPUs, and the SEMACALL can run concurrently on different > >> CPUs. Implement a mechanism to run SEAMCALL concurrently on all online > >> CPUs and use it to shut down the module. Later logical-cpu scope module > >> initialization will use it too. > > > > Uhh, those requirements ^ are not met by this: > > Can run concurrently != Must run concurrently > > The documentation clearly says "can run concurrently" as quoted above. The next sentense says: "Implement a mechanism to run SEAMCALL concurrently" -- it does not. Anyway, since we're all in agreement there is no such requirement at all, a schedule_on_each_cpu() might be more appropriate, there is no reason to use IPIs and spin-waiting for any of this. That said; perhaps we should grow: schedule_on_cpu(struct cpumask *cpus, work_func_t func); to only disturb a given mask of CPUs.
