x86: find offset for crashkernel reservation automatically

This patch removes the need of the crashkernel=...@offset parameter to define
a fixed offset for crashkernel reservation. That feature can be used together
with a relocatable kernel where the kexec-tools relocate the kernel and
get the actual offset from /proc/iomem.

The use case is a kernel where the .text+.data+.bss is after 16M physical
memory (debug kernel with lockdep on x86_64 can cause that) which caused a
major pain in autoconfiguration in our distribution.

Also, that patch unifies crashdump architectures a bit since IA64 has
that semantics from the very beginning of the kdump port.
Signed-off-by: Bernhard Walle <bwalle@suse.de>
Cc: vgoyal@redhat.com
Cc: Bernhard Walle <bwalle@suse.de>
Cc: kexec@lists.infradead.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/setup.c

@@ -422,6 +422,34 @@ static void __init reserve_setup_data(void)
  */
 
 #ifdef CONFIG_KEXEC
+
+/**
+ * Reserve @size bytes of crashkernel memory at any suitable offset.
+ *
+ * @size: Size of the crashkernel memory to reserve.
+ * Returns the base address on success, and -1ULL on failure.
+ */
+unsigned long long find_and_reserve_crashkernel(unsigned long long size)
+{
+	const unsigned long long alignment = 16<<20; 	/* 16M */
+	unsigned long long start = 0LL;
+
+	while (1) {
+		int ret;
+
+		start = find_e820_area(start, ULONG_MAX, size, alignment);
+		if (start == -1ULL)
+			return start;
+
+		/* try to reserve it */
+		ret = reserve_bootmem_generic(start, size, BOOTMEM_EXCLUSIVE);
+		if (ret >= 0)
+			return start;
+
+		start += alignment;
+	}
+}
+
 static inline unsigned long long get_total_mem(void)
 {
 	unsigned long long total;
@@ -444,19 +472,26 @@ static void __init reserve_crashkernel(void)
 
 	ret = parse_crashkernel(boot_command_line, total_mem,
 			&crash_size, &crash_base);
-	if (ret == 0 && crash_size > 0) {
+	if (ret != 0 || crash_size <= 0)
+		return;
+
+	/* 0 means: find the address automatically */
 	if (crash_base <= 0) {
-			printk(KERN_INFO "crashkernel reservation failed - "
-					"you have to specify a base address\n");
+		crash_base = find_and_reserve_crashkernel(crash_size);
+		if (crash_base == -1ULL) {
+			pr_info("crashkernel reservation failed. "
+				"No suitable area found.\n");
 			return;
 		}
-
-		if (reserve_bootmem_generic(crash_base, crash_size,
-					BOOTMEM_EXCLUSIVE) < 0) {
-			printk(KERN_INFO "crashkernel reservation failed - "
+	} else {
+		ret = reserve_bootmem_generic(crash_base, crash_size,
+					BOOTMEM_EXCLUSIVE);
+		if (ret < 0) {
+			pr_info("crashkernel reservation failed - "
 				"memory is in use\n");
 			return;
 		}
+	}
 
 	printk(KERN_INFO "Reserving %ldMB of memory at %ldMB "
 			"for crashkernel (System RAM: %ldMB)\n",
@@ -467,7 +502,6 @@ static void __init reserve_crashkernel(void)
 	crashk_res.start = crash_base;
 	crashk_res.end   = crash_base + crash_size - 1;
 	insert_resource(&iomem_resource, &crashk_res);
-	}
 }
 #else
 static void __init reserve_crashkernel(void)