powerpc: Don't search for paca in freed memory

Starting with 0ba00dd5f05fef8b3b1ef2de853fcc708ebb140f (powerpc:
Dynamically allocate pacas) we free the memory for pacas beyond
cpu_possible, but we failed to update the loop the secondary cpus use
to find their paca.  If the system has running cpu threads for which
the kernel did not allocate a paca for they will search the memory that
was freed.  For instance this could happen when the device tree for
a kdump kernel was not updated after a cpu hotplug, or the kernel is
running with more cpus than the kernel was configured.

Since 7896e4f4dd4ce85e11edf1dc3946d86ce0a84d6e (powerpc: Set nr_cpu_ids
early and use it to free PACAs) we set nr_cpu_ids before telling the
cpus to advance, so use that to limit the search.

We can't reference nr_cpu_ids without CONFIG_SMP because it is defined
as 1 instead of a memory location, but any extra threads should be sent
to kexec_wait in that case anyways, so make that explicit and remove
the search loop for UP.

Note to stable: The fix also requires
7896e4f4dd4ce85e11edf1dc3946d86ce0a84d6e (powerpc: Set
nr_cpu_ids early and use it to free PACAs) to function.  Also
856548164958aed43b349cbd943ff7b55242232c (Properly handshake CPUs going
out of boot spin loop) affects the second chunk, specifically the branch
target was 3b before and is 4b after that patch, and there was a blank
line before the #ifdef CONFIG_SMP that was removed

Cc: <stable@kernel.org> # .34.x: 7896e4f4dd powerpc: Set nr_cpu_ids early
Cc: <stable@kernel.org> # .34.x
Signed-off-by: Milton Miller <miltonm@bga.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 73d6e9afcdf1466a3b407147fb9c96148f514199..ba504099844a1cd311cd6ae284bb1eaea092c985 100644 (file)
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -218,13 +218,19 @@ generic_secondary_common_init:
         */
        LOAD_REG_ADDR(r13, paca)        /* Load paca pointer             */
        ld      r13,0(r13)              /* Get base vaddr of paca array  */
+#ifndef CONFIG_SMP
+       addi    r13,r13,PACA_SIZE       /* know r13 if used accidentally */
+       b       .kexec_wait             /* wait for next kernel if !SMP  */
+#else
+       LOAD_REG_ADDR(r7, nr_cpu_ids)   /* Load nr_cpu_ids address       */
+       lwz     r7,0(r7)                /* also the max paca allocated   */
        li      r5,0                    /* logical cpu id                */
 1:     lhz     r6,PACAHWCPUID(r13)     /* Load HW procid from paca      */
        cmpw    r6,r24                  /* Compare to our id             */
        beq     2f
        addi    r13,r13,PACA_SIZE       /* Loop to next PACA on miss     */
        addi    r5,r5,1
-       cmpwi   r5,NR_CPUS
+       cmpw    r5,r7                   /* Check if more pacas exist     */
        blt     1b
 
        mr      r3,r24                  /* not found, copy phys to r3    */
@@ -259,9 +265,6 @@ generic_secondary_common_init:
 4:     HMT_LOW
        lbz     r23,PACAPROCSTART(r13)  /* Test if this processor should */
                                        /* start.                        */
-#ifndef CONFIG_SMP
-       b       4b                      /* Never go on non-SMP           */
-#else
        cmpwi   0,r23,0
        beq     4b                      /* Loop until told to go         */
 
@@ -273,7 +276,7 @@ generic_secondary_common_init:
        subi    r1,r1,STACK_FRAME_OVERHEAD
 
        b       __secondary_start
-#endif
+#endif /* SMP */
 
 /*
  * Turn the MMU off.