powerpc/powernv: Fix save/restore of SPRG3 on entry/exit from stop (idle)

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 (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: stable@vger.kernel.org # v4.14+
Reported-by: Florian Weimer <fweimer@redhat.com>
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>

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index e734f6e45abc1ecb64cc8fe68b88054210e30bd3..689306118b48641495ea3b7ad9f7b058b4ce14c8 100644 (file)
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -144,7 +144,9 @@ power9_restore_additional_sprs:
        mtspr   SPRN_MMCR1, r4
 
        ld      r3, STOP_MMCR2(r13)
+       ld      r4, PACA_SPRG_VDSO(r13)
        mtspr   SPRN_MMCR2, r3
+       mtspr   SPRN_SPRG3, r4
        blr
 
 /*