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Subject[086/103] powerpc: Dont use kernel stack with translation off
2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Michael Neuling <mikey@neuling.org>

commit 54a834043314c257210db2a9d59f8cc605571639 upstream.

In f761622e59433130bc33ad086ce219feee9eb961 we changed
early_setup_secondary so it's called using the proper kernel stack
rather than the emergency one.

Unfortunately, this stack pointer can't be used when translation is off
on PHYP as this stack pointer might be outside the RMO. This results in
the following on all non zero cpus:
cpu 0x1: Vector: 300 (Data Access) at [c00000001639fd10]
pc: 000000000001c50c
lr: 000000000000821c
sp: c00000001639ff90
msr: 8000000000001000
dar: c00000001639ffa0
dsisr: 42000000
current = 0xc000000016393540
paca = 0xc000000006e00200
pid = 0, comm = swapper
The original patch was only tested on bare metal system, so it never
caught this problem.

This changes __secondary_start so that we calculate the new stack
pointer but only start using it after we've called early_setup_secondary.

With this patch, the above problem goes away.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/powerpc/kernel/head_64.S | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -575,13 +575,19 @@ __secondary_start:
/* Initialize the kernel stack. Just a repeat for iSeries. */
LOAD_REG_ADDR(r3, current_set)
sldi r28,r24,3 /* get current_set[cpu#] */
- ldx r1,r3,r28
- addi r1,r1,THREAD_SIZE-STACK_FRAME_OVERHEAD
- std r1,PACAKSAVE(r13)
+ ldx r14,r3,r28
+ addi r14,r14,THREAD_SIZE-STACK_FRAME_OVERHEAD
+ std r14,PACAKSAVE(r13)

/* Do early setup for that CPU (stab, slb, hash table pointer) */
bl .early_setup_secondary

+ /*
+ * setup the new stack pointer, but *don't* use this until
+ * translation is on.
+ */
+ mr r1, r14
+
/* Clear backchain so we get nice backtraces */
li r7,0
mtlr r7



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