Re: [PATCH] powerpc/powernv : Save/Restore SPRG3 on entry/exit from stop.

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jul 23, 2018 at 08:16:28AM +0200, Greg KH wrote:
> On Mon, Jul 23, 2018 at 11:00:55AM +0530, Gautham R. Shenoy wrote:
> > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
> > 
> > [ Upstream commit b03897cf318dfc47de33a7ecbc7655584266f034 ]
> > 
> > On 64-bit servers, SPRN_SPRG3 and its userspace read-only mirror
> > SPRN_USPRG3 are used as userspace VDSO write and read registers
> > respectively.
> > 
> > SPRN_SPRG3 is lost when we enter stop4 and above, and is currently not
> > restored.  As a result, any read from SPRN_USPRG3 returns zero on an
> > exit from stop4 and above.
> > 
> > Thus in this situation, on POWER9, any call from sched_getcpu() always
> > returns zero, as on powerpc, we call __kernel_getcpu() which relies
> > upon SPRN_USPRG3 to report the CPU and NUMA node information.
> > 
> > Fix this by restoring SPRN_SPRG3 on wake up from a deep stop state
> > with the sprg_vdso value that is cached in PACA.
> > 
> > Fixes: e1c1cfed5432 ("powerpc/powernv: Save/Restore additional SPRs
> > for stop4 cpuidle")
> > 
> > Reported-by: Florian Weimer <fweimer@redhat.com>
> > Cc: <stable@vger.kernel.org> # 4.14
> > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> > Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
> > Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> > ---
> >  arch/powerpc/kernel/idle_book3s.S | 2 ++
> >  1 file changed, 2 insertions(+)
> 
> What stable tree(s) do you want this applied to?

I've now guessed that it is 4.14.y.  If that's not the case, please let
me know.

greg k-h