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

["Gautham R. Shenoy" <ego@linux.vnet.ibm.com>]

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(+)

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index 1125c9b..8959057 100644
--- 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
 	blr
 
 /*
-- 
1.9.4