Re: [PATCH v10 1/8] memory: prevent dma-reentracy issues

[Gerd Hoffmann]

  Hi,

> But I think unexpected access shouldn't be there in the 1st place,
> so guard looks pretty legit at this point.
> Lets see what Gerd finds out from edk2 point of view.

CPU eject happens /after/ SMM syncronisation, when CPUs are on their way
back into normal mode:

 * The boot processor will do the cpu hotplug register writes, from SMM
   mode, so it obviously will be in SMM mode still.
 * The processor to be unplugged will be parked in a halt loop in SMM
   mode until the unplug completed, so that processor will be in SMM
   mode too.
 * All other processors may or may not be in SMM mode.

So parallel access is possible.

take care,
  Gerd