[PATCH v3] Load crash kernel high on x86

[Petr Tesarik <ptesarik@suse.com>]

There may be more than one crash kernel regions on x86. Currently,
kexec-tools picks the largest one. If high reservation is smaller
than low, it will try to load panic kernel low. However, the kexec
syscall checks that target address is within crashk_res boundaries,
so attempts to load crash kernel low result in -EADDRNOTAVAIL, and
kexec prints out this error message:

kexec_load failed: Cannot assign requested address

Looking at the logic in arch/x86/kernel/setup.c, there are only two
possible layouts:

  1. crashk_res is below 4G, and there is only one region,
  2. crashk_res is above 4G, and crashk_low_res is below 4G

In either case, kexec-tools must pick the highest region.

Changelog:

  * v3: rename function to get_crash_kernel_load_range
  * v2: remove unnecessary local variables

Signed-off-by: Petr Tesarik <ptesarik@suse.com>

---
 kexec/arch/i386/crashdump-x86.c    | 21 +++++++--------------
 kexec/arch/i386/kexec-x86-common.c |  4 ++--
 kexec/kexec.h                      |  2 +-
 3 files changed, 10 insertions(+), 17 deletions(-)

diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
index 63959b7..d4969c5 100644
--- a/kexec/arch/i386/crashdump-x86.c
+++ b/kexec/arch/i386/crashdump-x86.c
@@ -1026,24 +1026,17 @@ int load_crashdump_segments(struct kexec_info *info, char* mod_cmdline,
 	return 0;
 }
 
-int get_max_crash_kernel_limit(uint64_t *start, uint64_t *end)
+/* On x86, the kernel may make a low reservation in addition to the
+ * normal reservation. However, the kernel refuses to load the panic
+ * kernel to low memory, so always choose the highest range.
+ */
+int get_crash_kernel_load_range(uint64_t *start, uint64_t *end)
 {
-	int i, idx = -1;
-	unsigned long sz_max = 0, sz;
-
 	if (!crash_reserved_mem_nr)
 		return -1;
 
-	for (i = crash_reserved_mem_nr - 1; i >= 0; i--) {
-		sz = crash_reserved_mem[i].end - crash_reserved_mem[i].start +1;
-		if (sz <= sz_max)
-			continue;
-		sz_max = sz;
-		idx = i;
-	}
-
-	*start = crash_reserved_mem[idx].start;
-	*end = crash_reserved_mem[idx].end;
+	*start = crash_reserved_mem[crash_reserved_mem_nr - 1].start;
+	*end = crash_reserved_mem[crash_reserved_mem_nr - 1].end;
 
 	return 0;
 }
diff --git a/kexec/arch/i386/kexec-x86-common.c b/kexec/arch/i386/kexec-x86-common.c
index 041c8ec..484d712 100644
--- a/kexec/arch/i386/kexec-x86-common.c
+++ b/kexec/arch/i386/kexec-x86-common.c
@@ -371,9 +371,9 @@ int get_memory_ranges(struct memory_range **range, int *ranges,
 	    !(kexec_flags & KEXEC_PRESERVE_CONTEXT)) {
 		uint64_t start, end;
 
-		ret = get_max_crash_kernel_limit(&start, &end);
+		ret = get_crash_kernel_load_range(&start, &end);
 		if (ret != 0) {
-			fprintf(stderr, "get_max_crash_kernel_limit failed.\n");
+			fprintf(stderr, "get_crash_kernel_load_range failed.\n");
 			return -1;
 		}
 
diff --git a/kexec/kexec.h b/kexec/kexec.h
index 0fa977f..7c97b25 100644
--- a/kexec/kexec.h
+++ b/kexec/kexec.h
@@ -288,7 +288,7 @@ int arch_process_options(int argc, char **argv);
 int arch_compat_trampoline(struct kexec_info *info);
 void arch_update_purgatory(struct kexec_info *info);
 int is_crashkernel_mem_reserved(void);
-int get_max_crash_kernel_limit(uint64_t *start, uint64_t *end);
+int get_crash_kernel_load_range(uint64_t *start, uint64_t *end);
 char *get_command_line(void);
 
 int kexec_iomem_for_each_line(char *match,
-- 
2.1.4

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