powerpc/kexec_file: Setup backup region for kdump kernel

Though kdump kernel boots from loaded address, the first 64KB of it is
copied down to real 0. So, setup a backup region and let purgatory
copy the first 64KB of crashed kernel into this backup region before
booting into kdump kernel. Update reserve map with backup region and
crashed kernel's memory to avoid kdump kernel from accidentially using
that memory.

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/159602294718.575379.16216507537038008623.stgit@hbathini

1 files changed, 90 insertions, 3 deletions

diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
index f94660874765..a81bffb72cc5 100644
--- a/arch/powerpc/kexec/file_load_64.c
+++ b/arch/powerpc/kexec/file_load_64.c
@@ -20,8 +20,10 @@
 #include <linux/of_device.h>
 #include <linux/memblock.h>
 #include <linux/slab.h>
+#include <linux/vmalloc.h>
 #include <asm/drmem.h>
 #include <asm/kexec_ranges.h>
+#include <asm/crashdump-ppc64.h>
 
 struct umem_info {
 	u64 *buf;		/* data buffer for usable-memory property */
@@ -606,6 +608,70 @@ out:
 }
 
 /**
+ * load_backup_segment - Locate a memory hole to place the backup region.
+ * @image:               Kexec image.
+ * @kbuf:                Buffer contents and memory parameters.
+ *
+ * Returns 0 on success, negative errno on error.
+ */
+static int load_backup_segment(struct kimage *image, struct kexec_buf *kbuf)
+{
+	void *buf;
+	int ret;
+
+	/*
+	 * Setup a source buffer for backup segment.
+	 *
+	 * A source buffer has no meaning for backup region as data will
+	 * be copied from backup source, after crash, in the purgatory.
+	 * But as load segment code doesn't recognize such segments,
+	 * setup a dummy source buffer to keep it happy for now.
+	 */
+	buf = vzalloc(BACKUP_SRC_SIZE);
+	if (!buf)
+		return -ENOMEM;
+
+	kbuf->buffer = buf;
+	kbuf->mem = KEXEC_BUF_MEM_UNKNOWN;
+	kbuf->bufsz = kbuf->memsz = BACKUP_SRC_SIZE;
+	kbuf->top_down = false;
+
+	ret = kexec_add_buffer(kbuf);
+	if (ret) {
+		vfree(buf);
+		return ret;
+	}
+
+	image->arch.backup_buf = buf;
+	image->arch.backup_start = kbuf->mem;
+	return 0;
+}
+
+/**
+ * load_crashdump_segments_ppc64 - Initialize the additional segements needed
+ *                                 to load kdump kernel.
+ * @image:                         Kexec image.
+ * @kbuf:                          Buffer contents and memory parameters.
+ *
+ * Returns 0 on success, negative errno on error.
+ */
+int load_crashdump_segments_ppc64(struct kimage *image,
+				  struct kexec_buf *kbuf)
+{
+	int ret;
+
+	/* Load backup segment - first 64K bytes of the crashing kernel */
+	ret = load_backup_segment(image, kbuf);
+	if (ret) {
+		pr_err("Failed to load backup segment\n");
+		return ret;
+	}
+	pr_debug("Loaded the backup region at 0x%lx\n", kbuf->mem);
+
+	return 0;
+}
+
+/**
  * setup_purgatory_ppc64 - initialize PPC64 specific purgatory's global
  *                         variables and call setup_purgatory() to initialize
  *                         common global variable.
@@ -643,6 +709,11 @@ int setup_purgatory_ppc64(struct kimage *image, const void *slave_code,
 			goto out;
 	}
 
+	/* Tell purgatory where to look for backup region */
+	ret = kexec_purgatory_get_set_symbol(image, "backup_start",
+					     &image->arch.backup_start,
+					     sizeof(image->arch.backup_start),
+					     false);
 out:
 	if (ret)
 		pr_err("Failed to setup purgatory symbols");
@@ -674,7 +745,7 @@ int setup_new_fdt_ppc64(const struct kimage *image, void *fdt,
 
 	/*
 	 * Restrict memory usage for kdump kernel by setting up
-	 * usable memory ranges.
+	 * usable memory ranges and memory reserve map.
 	 */
 	if (image->type == KEXEC_TYPE_CRASH) {
 		ret = get_usable_memory_ranges(&umem);
@@ -687,13 +758,26 @@ int setup_new_fdt_ppc64(const struct kimage *image, void *fdt,
 			goto out;
 		}
 
-		/* Ensure we don't touch crashed kernel's memory */
-		ret = fdt_add_mem_rsv(fdt, 0, crashk_res.start);
+		/*
+		 * Ensure we don't touch crashed kernel's memory except the
+		 * first 64K of RAM, which will be backed up.
+		 */
+		ret = fdt_add_mem_rsv(fdt, BACKUP_SRC_END + 1,
+				      crashk_res.start - BACKUP_SRC_SIZE);
 		if (ret) {
 			pr_err("Error reserving crash memory: %s\n",
 			       fdt_strerror(ret));
 			goto out;
 		}
+
+		/* Ensure backup region is not used by kdump/capture kernel */
+		ret = fdt_add_mem_rsv(fdt, image->arch.backup_start,
+				      BACKUP_SRC_SIZE);
+		if (ret) {
+			pr_err("Error reserving memory for backup: %s\n",
+			       fdt_strerror(ret));
+			goto out;
+		}
 	}
 
 out:
@@ -800,5 +884,8 @@ int arch_kimage_file_post_load_cleanup(struct kimage *image)
 	kfree(image->arch.exclude_ranges);
 	image->arch.exclude_ranges = NULL;
 
+	vfree(image->arch.backup_buf);
+	image->arch.backup_buf = NULL;
+
 	return kexec_image_post_load_cleanup_default(image);
 }