[kexec-tools][PATCH v2] zImage-arm: bugfix: kernel offset must be 0x8000

[Wang Nan]

This patch fixs a problem introduced by commit e5d6a55 which make ARM
kexec fails.

Due to that commit, kernel is loaded at a dynamically offset: it computes
extra_size using size of dtb, and load zImage at base + extra_size. When
dtb size small (for example, 0x3000 bytes), kernel will be loaded at
address like 0x60003000. For ARM zImage such address is incorrect.

In kernel code arch/arm/boot/compressed/head.S, zImage builds a
temporary page table at (pc & 0xf8000000) + TEXT_OFFSET - 0x4000. The
related instructions sequence is:

 mov     r4, pc
 and     r4, r4, #0xf8000000
 add     r4, r4, #TEXT_OFFSET @ (TEXT_OFFSET == 0x8000 on most platforms)
 call cache_on
   ...
   call __armv7_mmu_cache_on
     ...
     call __setup_mmu
       sub     r3, r4, #16384          @ Page directory size

r3 becomes page table pointer.

When kernel is loaded at 0x60003000, page table is still built at
0x60004000, which destroys kernel.

This patch make extra_size a fix value (0x8000) to avoid the failure.

For the problem commit e5d6a55 tries solve, this patch uses
locate_holes() to find a place can hold initrd and dtb.

Change from v1:
 - Coding style enhancements.

Signed-off-by: Wang Nan <wangnan0 at huawei.com>
Cc: Daniel Mack <zonque at gmail.com>
Cc: Sven Neumann <s.neumann at raumfeld.com>
Cc: Simon Horman <horms at verge.net.au>
---
 kexec/arch/arm/kexec-zImage-arm.c | 37 +++++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

diff --git a/kexec/arch/arm/kexec-zImage-arm.c b/kexec/arch/arm/kexec-zImage-arm.c
index 4b5d3f4..bc99e79 100644
--- a/kexec/arch/arm/kexec-zImage-arm.c
+++ b/kexec/arch/arm/kexec-zImage-arm.c
@@ -282,7 +282,7 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 {
 	unsigned long base;
 	unsigned int atag_offset = 0x1000; /* 4k offset from memory start */
-	unsigned int extra_size = 0;
+	unsigned int extra_size = 0x8000; /* TEXT_OFFSET */
 	const char *command_line;
 	char *modified_cmdline = NULL;
 	off_t command_line_len;
@@ -356,16 +356,11 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 		if (command_line_len > COMMAND_LINE_SIZE)
 			command_line_len = COMMAND_LINE_SIZE;
 	}
-	if (ramdisk) {
+	if (ramdisk)
 		ramdisk_buf = slurp_file(ramdisk, &initrd_size);
-	}
 
-	if (dtb_file) {
+	if (dtb_file)
 		dtb_buf = slurp_file(dtb_file, &dtb_length);
-		extra_size = _ALIGN(dtb_length, getpagesize());
-	} else if (use_atags) {
-		extra_size = 0x8000;	/* 32k should be plenty for ATAGs */
-	}
 
 	/*
 	 * If we are loading a dump capture kernel, we need to update kernel
@@ -460,6 +455,32 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 			create_flatten_tree(&dtb_buf, &dtb_length, command_line);
 		}
 
+		/*
+		 * Search in memory to make sure there is enough memory
+		 * to hold initrd and dtb.
+		 *
+		 * Even if no initrd is used, this check is still
+		 * required for dtb.
+		 *
+		 * Crash kernel use fixed address, no check is ok.
+		 */
+		if ((info->kexec_flags & KEXEC_ON_CRASH) == 0) {
+			unsigned long page_size = getpagesize();
+			/*
+			 * DTB size may be increase a little
+			 * when setup initrd size. Add a full page
+			 * for it is enough.
+			 */
+			unsigned long hole_size = _ALIGN_UP(initrd_size, page_size) +
+				_ALIGN(dtb_length + page_size, page_size);
+			unsigned long initrd_base_new = locate_hole(info,
+					hole_size, page_size,
+					initrd_base, ULONG_MAX, INT_MAX);
+			if (base == ULONG_MAX)
+				return -1;
+			initrd_base = initrd_base_new;
+		}
+
 		if (ramdisk) {
 			add_segment(info, ramdisk_buf, initrd_size,
 			            initrd_base, initrd_size);
-- 
1.8.3.4