On Wed, 2018-07-18 at 08:33:16 UTC, "Gautham R. Shenoy" wrote:
> From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com>
>
> 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 <fwei...@redhat.com>
> Cc: <sta...@vger.kernel.org> # 4.14
> Cc: Oleg Nesterov <o...@redhat.com>
> Cc: Michael Neuling <mi...@neuling.org>
> Cc: Michael Ellerman <m...@ellerman.id.au>
> Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
> Cc: Vaidyanathan Srinivasan <sva...@linux.vnet.ibm.com>
> Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
Applied to powerpc fixes, thanks.
https://git.kernel.org/powerpc/c/b03897cf318dfc47de33a7ecbc7655
cheers
