Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of error

[Peter Zijlstra]

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.