From: "Gautham R. Shenoy" ego@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 fweimer@redhat.com Cc: stable@vger.kernel.org # 4.14 Cc: Oleg Nesterov oleg@redhat.com Cc: Michael Neuling mikey@neuling.org Cc: Michael Ellerman mpe@ellerman.id.au Cc: Benjamin Herrenschmidt benh@kernel.crashing.org Cc: Vaidyanathan Srinivasan svaidy@linux.vnet.ibm.com Signed-off-by: Gautham R. Shenoy ego@linux.vnet.ibm.com --- Change from v1: Restoring the SPRG3 from paca->sprg_vdso instead of saving it separately during stop-entry, as suggested by Mikey.

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 d85d551..672ead8 100644 --- 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

/*