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> --- 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 /* -- 1.8.3.1