[PATCH] ppc64: dynamically allocate emergency stacks

Now we set up cpu_possible_map early we can dynamically allocate the
emergency stacks.  Previously we would allocate NR_CPUS * PAGE_SIZE,
potentially wasting quite a lot of memory.

Clean a comment up in irqstack_early_init and use unsigned int for cpu ids
while in the area.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc64/kernel/pacaData.c

@@ -27,13 +27,6 @@ struct systemcfg *systemcfg;
  * field correctly */
 extern unsigned long __toc_start;
 
-/* Stack space used when we detect a bad kernel stack pointer, and
- * early in SMP boots before relocation is enabled.
- *
- * ABI requires stack to be 128-byte aligned
- */
-char emergency_stack[PAGE_SIZE * NR_CPUS] __attribute__((aligned(128)));
-
 /* The Paca is an array with one entry per processor.  Each contains an 
  * ItLpPaca, which contains the information shared between the 
  * hypervisor and Linux.  Each also contains an ItLpRegSave area which
@@ -55,7 +48,6 @@ char emergency_stack[PAGE_SIZE * NR_CPUS] __attribute__((aligned(128)));
 	.kernel_toc = (unsigned long)(&__toc_start) + 0x8000UL,		    \
 	.stab_real = (asrr), 		/* Real pointer to segment table */ \
 	.stab_addr = (asrv),		/* Virt pointer to segment table */ \
-	.emergency_sp = &emergency_stack[((number)+1) * PAGE_SIZE],	    \
 	.cpu_start = (start),		/* Processor start */		    \
 	.lppaca = {							    \
 		.xDesc = 0xd397d781,	/* "LpPa" */			    \

arch/ppc64/kernel/setup.c

@@ -701,9 +701,12 @@ extern void (*calibrate_delay)(void);
 #ifdef CONFIG_IRQSTACKS
 static void __init irqstack_early_init(void)
 {
-	int i;
+	unsigned int i;
 
-	/* interrupt stacks must be under 256MB, we cannot afford to take SLB misses on them */
+	/*
+	 * interrupt stacks must be under 256MB, we cannot afford to take
+	 * SLB misses on them.
+	 */
 	for_each_cpu(i) {
 		softirq_ctx[i] = (struct thread_info *)__va(lmb_alloc_base(THREAD_SIZE,
 					THREAD_SIZE, 0x10000000));
@@ -715,6 +718,24 @@ static void __init irqstack_early_init(void)
 #define irqstack_early_init()
 #endif
 
+/*
+ * Stack space used when we detect a bad kernel stack pointer, and
+ * early in SMP boots before relocation is enabled.
+ */
+static void __init emergency_stack_init(void)
+{
+	unsigned int i;
+
+	/*
+	 * Emergency stacks must be under 256MB, we cannot afford to take
+	 * SLB misses on them. The ABI also requires them to be 128-byte
+	 * aligned.
+	 */
+	for_each_cpu(i)
+		paca[i].emergency_sp = __va(lmb_alloc_base(PAGE_SIZE, 128,
+						0x10000000)) + PAGE_SIZE;
+}
+
 /*
  * Called into from start_kernel, after lock_kernel has been called.
  * Initializes bootmem, which is unsed to manage page allocation until
@@ -761,6 +782,7 @@ void __init setup_arch(char **cmdline_p)
 	*cmdline_p = cmd_line;
 
 	irqstack_early_init();
+	emergency_stack_init();
 
 	/* set up the bootmem stuff with available memory */
 	do_init_bootmem();