linux-kernel - [PATCH] of: Fix comparison of reserved memory regions

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Date:	Wed, 18 Nov 2015 21:46:38 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	robh+dt@...nel.org
Cc:	devicetree@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	<linuxppc-dev@...abs.org>, mitchelh@...eaurora.org,
	frowand.list@...il.com, grant.likely@...aro.org
Subject: [PATCH] of: Fix comparison of reserved memory regions

In order to check for overlapping reserved memory regions, we first need
to sort the array of memory regions. This is implemented using sort(),
and a custom comparison function __rmem_cmp().

Unfortunatley __rmem_cmp() doesn't work in all cases. Because the two
base values are phys_addr_t, they may be u64 on some platforms, in which
case subtracting one from the other and then (implicitly) casting to int
does not give us the -ve/0/+ve value we need.

This leads to incorrect reports about overlaps, eg:

  ibm,slw-image@...e600000 (0x0000001ffe600000--0x0000001ffe700000) overlaps with
  ibm,firmware-allocs-memory@...0000000 (0x0000001000000000--0x0000001000dc0200)

Fix it by just doing the standard double if and return 0 logic.

Fixes: ae1add247bf8 ("of: Check for overlap in reserved memory regions")
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
---
 drivers/of/of_reserved_mem.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index be77e75c587d..1a3556a9e9ea 100644
--- a/drivers/of/of_reserved_mem.c
+++ b/drivers/of/of_reserved_mem.c
@@ -206,7 +206,13 @@ static int __init __rmem_cmp(const void *a, const void *b)
 {
 	const struct reserved_mem *ra = a, *rb = b;
 
-	return ra->base - rb->base;
+	if (ra->base < rb->base)
+		return -1;
+
+	if (ra->base > rb->base)
+		return 1;
+
+	return 0;
 }
 
 static void __init __rmem_check_for_overlap(void)
-- 
2.5.0

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