On Thu, Mar 31, 2016 at 09:12:32AM +0100, Marc Zyngier wrote: > On 31/03/16 08:57, AKASHI Takahiro wrote: > > On Mon, Mar 21, 2016 at 01:29:28PM +0000, James Morse wrote: > >> On 18/03/16 18:08, James Morse wrote: > >>> On 14/03/16 17:48, Geoff Levand wrote: > >>>> + /* just in case */ > >>>> + while (1) > >>>> + wfi(); > >> > >> Having thought about this some more: I don't think spinning like this is safe. > >> We need to spin with the MMU turned off, otherwise this core will pollute the > >> kdump kernel with TLB entries from the old page tables. > > > > I think that wfi() will never wake up since local interrupts are disabled > > here. So how can it pollute the kdump kernel? > > Having interrupts disabled doesn't prevent an exit from WFI. Quite the > opposite, actually. It is designed to wake-up the core when something > happens on the external interface. Further, WFI is a hint, and may simply act as a NOP. The ARM ARM calls this out (see "D1.17.2" Wait For Interrupt in ARM DDI 0487A.i): Because the architecture permits a PE to leave the low-power state for any reason, it is permissible for a PE to treat WFI as a NOP , but this is not recommended for lowest power operation. Thanks, Mark.
