Re: [PATCH] of: Fix reserved-memory overlap detection

[Vincent Whitchurch <vincent.whitchurch@axis.com>]

On Tue, Oct 20, 2020 at 03:00:14PM +0200, Rob Herring wrote:
> On Tue, Oct 20, 2020 at 2:36 AM Vincent Whitchurch
> <vincent.whitchurch@axis.com> wrote:
> >
> > The reserved-memory overlap detection code fails to detect overlaps if
> > either of the regions starts at address 0x0.  For some reason the code
> > explicitly checks for and ignores such regions, but this check looks
> > invalid.  Remove the check and fix this detection.
> 
> Wouldn't 'base' be 0 for nodes that have a 'size' and no address? The
> base in those cases isn't set until later when
> __reserved_mem_alloc_size() is called.

Ah, yes, I guess that's why the check was there.  I see that those
entries have both a zero address and a zero size, so this seems to work:

diff --git a/arch/arm/boot/dts/vexpress-v2p-ca9.dts b/arch/arm/boot/dts/vexpress-v2p-ca9.dts
index 623246f37448..6627e71c7283 100644
--- a/arch/arm/boot/dts/vexpress-v2p-ca9.dts
+++ b/arch/arm/boot/dts/vexpress-v2p-ca9.dts
@@ -81,6 +81,18 @@ vram: vram@4c000000 {
 			reg = <0x4c000000 0x00800000>;
 			no-map;
 		};
+
+		foo@0 {
+			reg = <0x0 0x2000>;
+		};
+
+		bar@1000 {
+			reg = <0x0 0x1000>;
+		};
+
+		baz {
+			size = <0x1000>;
+		};
 	};
 
 	clcd@10020000 {
diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index 46b9371c8a33..fea9433d942a 100644
--- a/drivers/of/of_reserved_mem.c
+++ b/drivers/of/of_reserved_mem.c
@@ -200,6 +200,16 @@ static int __init __rmem_cmp(const void *a, const void *b)
 	if (ra->base > rb->base)
 		return 1;
 
+	/*
+	 * Put the dynamic allocations (address == 0, size == 0) before static
+	 * allocations at address 0x0 so that overlap detection works
+	 * correctly.
+	 */
+	if (ra->size < rb->size)
+		return -1;
+	if (ra->size > rb->size)
+		return 1;
+
 	return 0;
 }
 
@@ -212,13 +222,19 @@ static void __init __rmem_check_for_overlap(void)
 
 	sort(reserved_mem, reserved_mem_count, sizeof(reserved_mem[0]),
 	     __rmem_cmp, NULL);
+
+	for (i = 0; i < reserved_mem_count - 1; i++) {
+		struct reserved_mem *this = &reserved_mem[i];
+
+		pr_info("i %d base %x size %x\n", i, this->base, this->size);
+	}
+
 	for (i = 0; i < reserved_mem_count - 1; i++) {
 		struct reserved_mem *this, *next;
 
 		this = &reserved_mem[i];
 		next = &reserved_mem[i + 1];
-		if (!(this->base && next->base))
-			continue;
+
 		if (this->base + this->size > next->base) {
 			phys_addr_t this_end, next_end;