powerpc: Allow duplicate lmb_reserve() calls

powerpc: Allow duplicate lmb_reserve() calls

[David Gibson]

Paulus, please apply.

At present calling lmb_reserve() (and hence lmb_add_region()) twice
for exactly the same memory region will cause strange behaviour.

This makes life difficult when booting from a flat device tree with
memory reserve map.  Which regions are automatically reserved by the
kernel has changed over time, so it's quite possible a newer kernel
could attempt to auto-reserve a region which is also explicitly listed
in the device tree's reserve map, leading to trouble.

This patch avoids the problem by making lmb_reserve() ignore a call to
reserve a previously reserved region.  It also removes a now redundant
test designed to avoid one specific case of the problem noted above.

At present, this patch deals only with duplicate reservations of an
identical region.  Attempting to reserve two different, but
overlapping regions will still cause problems.  I might post another
patch later dealing with this case, but I'm avoiding it now since it
is substantially more complicated to deal with, less likely to occur
and more likely to indicate a genuine bug elsewhere if it does occur.

Signed-off-by: David Gibson <dwg@au1.ibm.com>


Index: working-2.6/arch/powerpc/mm/lmb.c
===================================================================
--- working-2.6.orig/arch/powerpc/mm/lmb.c	2007-02-06 16:21:02.000000000 +1100
+++ working-2.6/arch/powerpc/mm/lmb.c	2007-02-06 16:22:32.000000000 +1100
@@ -146,6 +146,10 @@ static long __init lmb_add_region(struct
 		unsigned long rgnbase = rgn->region[i].base;
 		unsigned long rgnsize = rgn->region[i].size;
 
+		if ((rgnbase == base) && (rgnsize == size))
+			/* Already have this region, so we're done */
+			return 0;
+
 		adjacent = lmb_addrs_adjacent(base,size,rgnbase,rgnsize);
 		if ( adjacent > 0 ) {
 			rgn->region[i].base -= size;
Index: working-2.6/arch/powerpc/kernel/prom.c
===================================================================
--- working-2.6.orig/arch/powerpc/kernel/prom.c	2007-02-06 16:22:48.000000000 +1100
+++ working-2.6/arch/powerpc/kernel/prom.c	2007-02-06 16:22:57.000000000 +1100
@@ -954,9 +954,6 @@ static void __init early_reserve_mem(voi
 		size = *(reserve_map++);
 		if (size == 0)
 			break;
-		/* skip if the reservation is for the blob */
-		if (base == self_base && size == self_size)
-			continue;
 		DBG("reserving: %llx -> %llx\n", base, size);
 		lmb_reserve(base, size);
 	}

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson