[PATCH v2 1/3] kho: walk bootmem areas in address order

["Mike Rapoport (Microsoft)" <rppt@kernel.org>]

kexec_add_buffer() users may depend on the order in which memory holes are
searched. For instance, arm64 places the kernel bottom-up and then
requires the DTB to be above the kernel.

kho_walk_bootmem() walks the bootmem areas in the order they were
reserved, so if the kernel lands in a small area at the top of the memory
there is no room left for the DTB and kexec fails. For example, on an
arm64 VM with 2G of RAM and kho_bootmem=8M,64M,64M, the lowmem area is
reserved first at the top of the memory, the kernel image takes most of
it and kexec fails with

  kexec_file(Image): Could not find any suitable kernel location!

Sort the bootmem areas by address and walk them in ascending order, or in
descending order for top-down searches, like kexec_walk_resources() does.

Fixes: 3bdecc3c93f9 ("kexec: add KHO support to kexec file loads")
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 kernel/liveupdate/kexec_handover.c | 57 ++++++++++++++++++++++++++++++--------
 1 file changed, 46 insertions(+), 11 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 6f1f55fe31819..2ac5d94f33fd4 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -26,6 +26,7 @@
 #include <linux/list.h>
 #include <linux/memblock.h>
 #include <linux/page-isolation.h>
+#include <linux/sort.h>
 #include <linux/unaligned.h>
 #include <linux/vmalloc.h>
 
@@ -820,6 +821,14 @@ bool kho_bootmem_overlap(phys_addr_t phys, size_t size)
 	return false;
 }
 
+static int __init kho_bootmem_cmp(const void *_a, const void *_b)
+{
+	const struct kho_bootmem *a = _a;
+	const struct kho_bootmem *b = _b;
+
+	return cmp_int(a->addr, b->addr);
+}
+
 /**
  * kho_reserve_bootmem - Reserve a contiguous chunk of memory for kexec
  *
@@ -904,6 +913,9 @@ static void __init kho_reserve_bootmem(void)
 	 */
 	kho_bootmem_cnt = i;
 
+	sort(kho_bootmem, kho_bootmem_cnt, sizeof(*kho_bootmem),
+	     kho_bootmem_cmp, NULL);
+
 	return;
 
 err_free_bootmem_areas:
@@ -2081,20 +2093,40 @@ int kho_fill_kimage(struct kimage *image)
 	return 0;
 }
 
-static int kho_walk_bootmem(struct kexec_buf *kbuf,
-			    int (*func)(struct resource *, void *))
+static int kho_bootmem_walk_one(struct kexec_buf *kbuf,
+				const struct kho_bootmem *area,
+				int (*func)(struct resource *, void *))
+{
+	struct resource res = {
+		.start = area->addr,
+		.end = area->addr + area->size - 1,
+	};
+
+	/* Try to fit the kbuf into our KHO bootmem region */
+	return func(&res, kbuf);
+}
+
+static int kho_bootmem_walk_top_down(struct kexec_buf *kbuf,
+				     int (*func)(struct resource *, void *))
 {
 	int ret = 0;
-	int i;
 
-	for (i = 0; i < kho_bootmem_cnt; i++) {
-		struct resource res = {
-			.start = kho_bootmem[i].addr,
-			.end = kho_bootmem[i].addr + kho_bootmem[i].size - 1,
-		};
+	for (int i = kho_bootmem_cnt - 1; i >= 0; i--) {
+		ret = kho_bootmem_walk_one(kbuf, &kho_bootmem[i], func);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
 
-		/* Try to fit the kimage into our KHO bootmem region */
-		ret = func(&res, kbuf);
+static int kho_bootmem_walk_bottom_up(struct kexec_buf *kbuf,
+				      int (*func)(struct resource *, void *))
+{
+	int ret = 0;
+
+	for (int i = 0; i < kho_bootmem_cnt; i++) {
+		ret = kho_bootmem_walk_one(kbuf, &kho_bootmem[i], func);
 		if (ret)
 			break;
 	}
@@ -2110,7 +2142,10 @@ int kho_locate_mem_hole(struct kexec_buf *kbuf,
 	if (!kho_enable || kbuf->image->type == KEXEC_TYPE_CRASH)
 		return 1;
 
-	ret = kho_walk_bootmem(kbuf, func);
+	if (kbuf->top_down)
+		ret = kho_bootmem_walk_top_down(kbuf, func);
+	else
+		ret = kho_bootmem_walk_bottom_up(kbuf, func);
 
 	return ret == 1 ? 0 : -EADDRNOTAVAIL;
 }

-- 
2.53.0