On Tue, Feb 19, 2019 at 02:13:51PM +1000, Nicholas Piggin wrote: > Paul Mackerras's on February 18, 2019 9:06 am: > > On Sat, Oct 13, 2018 at 10:04:09PM +1000, Nicholas Piggin wrote: > >> Reimplement Book3S idle code in C, moving POWER7/8/9 implementation > >> speific HV idle code to the powernv platform code. > >> > > > > [...] > > > >> @@ -2760,21 +2744,47 @@ BEGIN_FTR_SECTION > >> li r4, LPCR_PECE_HVEE@higher > >> sldi r4, r4, 32 > >> or r5, r5, r4 > >> -END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300) > >> +FTR_SECTION_ELSE > >> + li r3, PNV_THREAD_NAP > >> +ALT_FTR_SECTION_END_IFSET(CPU_FTR_ARCH_300) > >> mtspr SPRN_LPCR,r5 > >> isync > >> - li r0, 0 > >> - std r0, HSTATE_SCRATCH0(r13) > >> - ptesync > >> - ld r0, HSTATE_SCRATCH0(r13) > >> -1: cmpd r0, r0 > >> - bne 1b > >> + > >> + mr r0, r1 > >> + ld r1, PACAEMERGSP(r13) > >> + subi r1, r1, STACK_FRAME_OVERHEAD > >> + std r0, 0(r1) > >> + ld r0, PACAR1(r13) > >> + std r0, 8(r1) > > > > This bit seems wrong to me. If this is a secondary thread on POWER8, > > we were already on the emergency stack, and now we've reset r1 back to > > the top of the emergency stack and we're overwriting it. > > I'll have to find some time to take another look at this stuff. The KVM > stuff was a bit hasty. > > > I wonder why you didn't see secondary threads going off into lala land > > in your tests? > > It must have been because I wasn't testing the guest SMT properly > because I did get it to break trivially sometime after posting this > patch out. So we were on the emergency stack here, that should make > things easier, that may be what's wrong.
In fact I don't see why you need to load up a new stack here at all; you could just use whatever stack we're currently on AFAICS. Paul.
