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

[Greg KH <gregkh@linuxfoundation.org>]

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?

thanks,

greg k-h