Subject: Re: [v2] powerpc/powernv : Save/Restore SPRG3 on entry/exit from stop.

From: Michael Ellerman <[email-masked]>
Date: Thu, 19 Jul 2018 16:06:10 +1000 (AEST)

On Wed, 2018-07-18 at 08:33:16 UTC, "Gautham R. Shenoy" wrote:
> From: "Gautham R. Shenoy" <[email-masked]>
> 
> 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 <[email-masked]>
> Cc: <[email-masked]> # 4.14
> Cc: Oleg Nesterov <[email-masked]>
> Cc: Michael Neuling <[email-masked]>
> Cc: Michael Ellerman <[email-masked]>
> Cc: Benjamin Herrenschmidt <[email-masked]>
> Cc: Vaidyanathan Srinivasan <[email-masked]>
> Signed-off-by: Gautham R. Shenoy <[email-masked]>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/b03897cf318dfc47de33a7ecbc7655

cheers