On Tue, 2018-09-25 at 22:00 +1000, Michael Ellerman wrote: > Michael Neuling <mi...@neuling.org> writes: > > Current we store the userspace r1 to PACATMSCRATCH before finally > > saving it to the thread struct. > > > > In theory an exception could be taken here (like a machine check or > > SLB miss) that could write PACATMSCRATCH and hence corrupt the > > userspace r1. The SLB fault currently doesn't touch PACATMSCRATCH, but > > others do. > > > > We've never actually seen this happen but it's theoretically > > possible. Either way, the code is fragile as it is. > > > > This patch saves r1 to the kernel stack (which can't fault) before we > > turn MSR[RI] back on. PACATMSCRATCH is still used but only with > > MSR[RI] off. We then copy r1 from the kernel stack to the thread > > struct once we have MSR[RI] back on. > > > > Suggested-by: Breno Leitao <lei...@debian.org> > > Signed-off-by: Michael Neuling <mi...@neuling.org> > > --- > > arch/powerpc/kernel/tm.S | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/arch/powerpc/kernel/tm.S b/arch/powerpc/kernel/tm.S > > index 701b0f5b09..8207816a1e 100644 > > --- a/arch/powerpc/kernel/tm.S > > +++ b/arch/powerpc/kernel/tm.S > > @@ -178,6 +178,12 @@ _GLOBAL(tm_reclaim) > > > > std r11, GPR11(r1) /* Temporary stash */ > > > > + /* Move r1 to kernel stack in case PACATMSCRATCH is used once > > + * we turn on RI > > + */ > > I see we still need to send you to Comment Formatting Re-Education Camp.
The rest of that file has they style, so I'm just keeping with that. I can submit a patch later to fix them all up. > I rewrote it a bit too, to hopefully be clearer? > > /* > * Move the saved user r1 to the kernel stack in case PACATMSCRATCH is > * clobbered by an exception once we turn on MSR_RI below. > */ > ld r11, PACATMSCRATCH(r13) > std r11, GPR1(r1) Yeah, that's clearer... thanks. Mikey
