> On May 31, 2019, at 2:05 PM, Jiri Kosina <ji...@kernel.org> wrote: > >> On Fri, 31 May 2019, Andy Lutomirski wrote: >> >> The Intel SDM Vol 3 34.10 says: >> >> If the HLT instruction is restarted, the processor will generate a >> memory access to fetch the HLT instruction (if it is >> not in the internal cache), and execute a HLT bus transaction. This >> behavior results in multiple HLT bus transactions >> for the same HLT instruction. > > Which basically means that both hibernation and kexec have been broken in > this respect for gazillions of years, and seems like noone noticed. Makes > one wonder what the reason for that might be. > > Either SDM is not precise and the refetch actually never happens for real > (or is always in these cases satisfied from I$ perhaps?), or ... ? > > So my patch basically puts things back where they have been for ages > (while mwait is obviously much worse, as that gets woken up by the write > to the monitored address, which inevitably does happen during resume), but > seems like SDM is suggesting that we've been in a grey zone wrt RSM at > least for all those ages. > > So perhaps we really should ditch resume_play_dead() altogether > eventually, and replace it with sending INIT IPI around instead (and then > waking the CPUs properly via INIT INIT START). I'd still like to do that > for 5.3 though, as that'd be slightly bigger surgery, and conservatively > put things basically back to state they have been up to now for 5.2. >
Seems reasonable to me. I would guess that it mostly works because SMI isn’t all that common and the window where it matters is short. Or maybe the SDM is misleading.
