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Subject[PATCH 4.14 43/44] powerpc/powernv: Fix save/restore of SPRG3 on entry/exit from stop (idle)
4.14-stable review patch.  If anyone has any objections, please let me know.


From: Gautham R. Shenoy <>

commit b03897cf318dfc47de33a7ecbc7655584266f034 upstream.

On 64-bit servers, SPRN_SPRG3 and its userspace read-only mirror
SPRN_USPRG3 are used as userspace VDSO write and read registers

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 (Power9 only) 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")
Cc: # v4.14+
Reported-by: Florian Weimer <>
Signed-off-by: Gautham R. Shenoy <>
Reviewed-by: Michael Ellerman <>
Signed-off-by: Michael Ellerman <>
Signed-off-by: Greg Kroah-Hartman <>

arch/powerpc/kernel/idle_book3s.S | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -140,6 +140,8 @@ power9_restore_additional_sprs:
ld r4, STOP_MMCR2(r13)
mtspr SPRN_MMCR1, r3
mtspr SPRN_MMCR2, r4
+ ld r4, PACA_SPRG_VDSO(r13)
+ mtspr SPRN_SPRG3, r4


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