[PATCH] kexec: Enable runtime allocation of crash_image

[Ricardo Ribalda]

Usually crash_image is defined statically via the crashkernel parameter
or DT.

But if the crash kernel is not used, or is smaller than then
area pre-allocated that memory is wasted.

Also, if the crash kernel was not defined at bootime, there is no way to
use the crash kernel.

Enable runtime allocation of the crash_image if the crash_image is not
defined statically. Following the same memory allocation/validation path
that for the reboot kexec kernel.

Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
kexec: Enable runtime allocation of crash_image

To: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: kexec@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Ross Zwisler <zwisler@xxxxxxxxxx>
Cc: Philipp Rudo <prudo@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
---
 include/linux/kexec.h | 1 +
 kernel/kexec.c        | 9 +++++----
 kernel/kexec_core.c   | 5 +++++
 kernel/kexec_file.c   | 7 ++++---
 4 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 41a686996aaa..98ca9a32bc8e 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -427,6 +427,7 @@ extern int kexec_load_disabled;
 extern bool kexec_in_progress;
 
 int crash_shrink_memory(unsigned long new_size);
+bool __crash_memory_valid(void);
 ssize_t crash_get_memory_size(void);
 
 #ifndef arch_kexec_protect_crashkres
diff --git a/kernel/kexec.c b/kernel/kexec.c
index cb8e6e6f983c..b5c17db25e88 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -28,7 +28,7 @@ static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
 	struct kimage *image;
 	bool kexec_on_panic = flags & KEXEC_ON_CRASH;
 
-	if (kexec_on_panic) {
+	if (kexec_on_panic && __crash_memory_valid()) {
 		/* Verify we have a valid entry point */
 		if ((entry < phys_to_boot_phys(crashk_res.start)) ||
 		    (entry > phys_to_boot_phys(crashk_res.end)))
@@ -44,7 +44,7 @@ static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
 	image->nr_segments = nr_segments;
 	memcpy(image->segment, segments, nr_segments * sizeof(*segments));
 
-	if (kexec_on_panic) {
+	if (kexec_on_panic && __crash_memory_valid()) {
 		/* Enable special crash kernel control page alloc policy. */
 		image->control_page = crashk_res.start;
 		image->type = KEXEC_TYPE_CRASH;
@@ -101,7 +101,7 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
 
 	if (flags & KEXEC_ON_CRASH) {
 		dest_image = &kexec_crash_image;
-		if (kexec_crash_image)
+		if (kexec_crash_image && __crash_memory_valid())
 			arch_kexec_unprotect_crashkres();
 	} else {
 		dest_image = &kexec_image;
@@ -157,7 +157,8 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
 	image = xchg(dest_image, image);
 
 out:
-	if ((flags & KEXEC_ON_CRASH) && kexec_crash_image)
+	if ((flags & KEXEC_ON_CRASH) && kexec_crash_image &&
+	    __crash_memory_valid())
 		arch_kexec_protect_crashkres();
 
 	kimage_free(image);
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index ca2743f9c634..77083c9760fb 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -1004,6 +1004,11 @@ void crash_kexec(struct pt_regs *regs)
 	}
 }
 
+bool __crash_memory_valid(void)
+{
+	return crashk_res.end != crashk_res.start;
+}
+
 ssize_t crash_get_memory_size(void)
 {
 	ssize_t size = 0;
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 45637511e0de..0671f4f370ff 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -280,7 +280,7 @@ kimage_file_alloc_init(struct kimage **rimage, int kernel_fd,
 
 	image->file_mode = 1;
 
-	if (kexec_on_panic) {
+	if (kexec_on_panic && __crash_memory_valid()) {
 		/* Enable special crash kernel control page alloc policy. */
 		image->control_page = crashk_res.start;
 		image->type = KEXEC_TYPE_CRASH;
@@ -345,7 +345,7 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 	dest_image = &kexec_image;
 	if (flags & KEXEC_FILE_ON_CRASH) {
 		dest_image = &kexec_crash_image;
-		if (kexec_crash_image)
+		if (kexec_crash_image && __crash_memory_valid())
 			arch_kexec_unprotect_crashkres();
 	}
 
@@ -408,7 +408,8 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 exchange:
 	image = xchg(dest_image, image);
 out:
-	if ((flags & KEXEC_FILE_ON_CRASH) && kexec_crash_image)
+	if ((flags & KEXEC_FILE_ON_CRASH) && kexec_crash_image &&
+	    __crash_memory_valid())
 		arch_kexec_protect_crashkres();
 
 	kexec_unlock();

---
base-commit: 4312098baf37ee17a8350725e6e0d0e8590252d4
change-id: 20221124-kexec-noalloc-3cab3cbe000f

Best regards,
-- 
Ricardo Ribalda <ribalda@xxxxxxxxxxxx>