[PATCH v2] arm64: kexec_file: try more regions if loading segments fails

[Benjamin Gwin]

It's possible that the first region picked for the new kernel will make
it impossible to fit the other segments in the required 32GB window,
especially if we have a very large initrd.

Instead of giving up, we can keep testing other regions for the kernel
until we find one that works.

Signed-off-by: Benjamin Gwin <bgwin at google.com>
Suggested-by: Ryan O'Leary <ryanoleary at google.com>
---
Fixing whitespace issues in previous revision

 arch/arm64/kernel/kexec_image.c        | 41 +++++++++++++++++++-------
 arch/arm64/kernel/machine_kexec_file.c |  9 +++++-
 2 files changed, 39 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
index af9987c154ca..66adee8b5fc8 100644
--- a/arch/arm64/kernel/kexec_image.c
+++ b/arch/arm64/kernel/kexec_image.c
@@ -43,7 +43,7 @@ static void *image_load(struct kimage *image,
 	u64 flags, value;
 	bool be_image, be_kernel;
 	struct kexec_buf kbuf;
-	unsigned long text_offset;
+	unsigned long text_offset, kernel_segment_number;
 	struct kexec_segment *kernel_segment;
 	int ret;
 
@@ -88,11 +88,37 @@ static void *image_load(struct kimage *image,
 	/* Adjust kernel segment with TEXT_OFFSET */
 	kbuf.memsz += text_offset;
 
-	ret = kexec_add_buffer(&kbuf);
-	if (ret)
+	kernel_segment_number = image->nr_segments;
+
+	/*
+	 * The location of the kernel segment may make it impossible to satisfy
+	 * the other segment requirements, so we try repeatedly to find a
+	 * location that will work.
+	 */
+	while ((ret = kexec_add_buffer(&kbuf)) == 0) {
+		/* Try to load additional data */
+		kernel_segment = &image->segment[kernel_segment_number];
+		ret = load_other_segments(image, kernel_segment->mem,
+					  kernel_segment->memsz, initrd,
+					  initrd_len, cmdline);
+		if (!ret)
+			break;
+
+		/*
+		 * We couldn't find space for the other segments; erase the
+		 * kernel segment and try the next available hole.
+		 */
+		image->nr_segments -= 1;
+		kbuf.buf_min = kernel_segment->mem + kernel_segment->memsz;
+		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
+	}
+
+	if (ret) {
+		pr_err("Could not find any suitable kernel location!");
 		return ERR_PTR(ret);
+	}
 
-	kernel_segment = &image->segment[image->nr_segments - 1];
+	kernel_segment = &image->segment[kernel_segment_number];
 	kernel_segment->mem += text_offset;
 	kernel_segment->memsz -= text_offset;
 	image->start = kernel_segment->mem;
@@ -101,12 +127,7 @@ static void *image_load(struct kimage *image,
 				kernel_segment->mem, kbuf.bufsz,
 				kernel_segment->memsz);
 
-	/* Load additional data */
-	ret = load_other_segments(image,
-				kernel_segment->mem, kernel_segment->memsz,
-				initrd, initrd_len, cmdline);
-
-	return ERR_PTR(ret);
+	return 0;
 }
 
 #ifdef CONFIG_KEXEC_IMAGE_VERIFY_SIG
diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index 5b0e67b93cdc..03210f644790 100644
--- a/arch/arm64/kernel/machine_kexec_file.c
+++ b/arch/arm64/kernel/machine_kexec_file.c
@@ -240,6 +240,11 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
 	return ret;
 }
 
+/*
+ * Tries to add the initrd and DTB to the image. If it is not possible to find
+ * valid locations, this function will undo changes to the image and return non
+ * zero.
+ */
 int load_other_segments(struct kimage *image,
 			unsigned long kernel_load_addr,
 			unsigned long kernel_size,
@@ -248,7 +253,8 @@ int load_other_segments(struct kimage *image,
 {
 	struct kexec_buf kbuf;
 	void *headers, *dtb = NULL;
-	unsigned long headers_sz, initrd_load_addr = 0, dtb_len;
+	unsigned long headers_sz, initrd_load_addr = 0, dtb_len,
+		      orig_segments = image->nr_segments;
 	int ret = 0;
 
 	kbuf.image = image;
@@ -334,6 +340,7 @@ int load_other_segments(struct kimage *image,
 	return 0;
 
 out_err:
+	image->nr_segments = orig_segments;
 	vfree(dtb);
 	return ret;
 }
-- 
2.29.1.341.ge80a0c044ae-goog