On Wed, 2018-07-18 at 08:33:16 UTC, "Gautham R. Shenoy" wrote:
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
Applied to powerpc fixes, thanks.
https://git.kernel.org/powerpc/c/b03897cf318dfc47de33a7ecbc7655
cheers