powerpc/smp: soft-replugged CPUs must go back to start_secondary
Various thing are torn down when a CPU is hot-unplugged. That CPU
is expected to go back to start_secondary when re-plugged to re
initialize everything, such as clock sources, maps, ...
Some implementations just return from cpu_die() callback
in the idle loop when the CPU is "re-plugged". This is not enough.
We fix it using a little asm trampoline which resets the stack
and calls back into start_secondary as if we were all fresh from
boot. The trampoline already existed on ppc64, but we add it for
ppc32
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 98c4b29..c5c24be 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -890,6 +890,15 @@
mtspr SPRN_SRR1,r4
SYNC
RFI
+
+_GLOBAL(start_secondary_resume)
+ /* Reset stack */
+ rlwinm r1,r1,0,0,(31-THREAD_SHIFT) /* current_thread_info() */
+ addi r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
+ li r3,0
+ std r3,0(r1) /* Zero the stack frame pointer */
+ bl start_secondary
+ b .
#endif /* CONFIG_SMP */
#ifdef CONFIG_KVM_BOOK3S_HANDLER