On Thu, Mar 31, 2016 at 11:10:38AM +0100, Mark Rutland wrote: > 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. Ah, OK. But even so, none of interrupt handlers (nor other code) will be executed after cpu wakes up, and the memory won't be polluted. Or do I still miss something? -Takahiro AKASHI > 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. -- Thanks, -Takahiro AKASHI
