[Qemu-devel] [PATCH v2] arm_boot: Change initrd load address to "halfway through RAM"

[Peter Maydell]

To avoid continually having to bump the initrd load address
to account for larger kernel images, put the initrd halfway
through RAM. This allows large kernels on new boards with lots
of RAM to work OK, without breaking existing usecases for
boards with only 32MB of RAM.

Note that this change fixes in passing a bug where we were
passing an overly large max_size to load_image_targphys()
for the initrd, which meant that we wouldn't correctly refuse
to load an enormous initrd that didn't actually fit into RAM.

Signed-off-by: Peter Maydell <address@hidden>
---
Changes v1->v2: put initrd at min(128M, ram_size / 2)
rather than just at ram_size / 2.

 hw/arm-misc.h |    1 +
 hw/arm_boot.c |   40 +++++++++++++++++++++++++---------------
 2 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/hw/arm-misc.h b/hw/arm-misc.h
index d02f7f0..adb1665 100644
--- a/hw/arm-misc.h
+++ b/hw/arm-misc.h
@@ -56,6 +56,7 @@ struct arm_boot_info {
                                      const struct arm_boot_info *info);
     /* Used internally by arm_boot.c */
     int is_linux;
+    hwaddr initrd_start;
     hwaddr initrd_size;
     hwaddr entry;
 };
diff --git a/hw/arm_boot.c b/hw/arm_boot.c
index 09bf6c5..92e2cab 100644
--- a/hw/arm_boot.c
+++ b/hw/arm_boot.c
@@ -18,7 +18,6 @@
 
 #define KERNEL_ARGS_ADDR 0x100
 #define KERNEL_LOAD_ADDR 0x00010000
-#define INITRD_LOAD_ADDR 0x00d00000
 
 /* The worlds second smallest bootloader.  Set r0-r2, then jump to kernel.  */
 static uint32_t bootloader[] = {
@@ -109,7 +108,7 @@ static void set_kernel_args(const struct arm_boot_info 
*info)
         /* ATAG_INITRD2 */
         WRITE_WORD(p, 4);
         WRITE_WORD(p, 0x54420005);
-        WRITE_WORD(p, info->loader_start + INITRD_LOAD_ADDR);
+        WRITE_WORD(p, info->initrd_start);
         WRITE_WORD(p, initrd_size);
     }
     if (info->kernel_cmdline && *info->kernel_cmdline) {
@@ -185,10 +184,11 @@ static void set_kernel_args_old(const struct 
arm_boot_info *info)
     /* pages_in_vram */
     WRITE_WORD(p, 0);
     /* initrd_start */
-    if (initrd_size)
-        WRITE_WORD(p, info->loader_start + INITRD_LOAD_ADDR);
-    else
+    if (initrd_size) {
+        WRITE_WORD(p, info->initrd_start);
+    } else {
         WRITE_WORD(p, 0);
+    }
     /* initrd_size */
     WRITE_WORD(p, initrd_size);
     /* rd_start */
@@ -281,14 +281,13 @@ static int load_dtb(hwaddr addr, const struct 
arm_boot_info *binfo)
 
     if (binfo->initrd_size) {
         rc = qemu_devtree_setprop_cell(fdt, "/chosen", "linux,initrd-start",
-                binfo->loader_start + INITRD_LOAD_ADDR);
+                binfo->initrd_start);
         if (rc < 0) {
             fprintf(stderr, "couldn't set /chosen/linux,initrd-start\n");
         }
 
         rc = qemu_devtree_setprop_cell(fdt, "/chosen", "linux,initrd-end",
-                    binfo->loader_start + INITRD_LOAD_ADDR +
-                    binfo->initrd_size);
+                    binfo->initrd_start + binfo->initrd_size);
         if (rc < 0) {
             fprintf(stderr, "couldn't set /chosen/linux,initrd-end\n");
         }
@@ -375,6 +374,19 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info 
*info)
     big_endian = 0;
 #endif
 
+    /* We want to put the initrd far enough into RAM that when the
+     * kernel is uncompressed it will not clobber the initrd. However
+     * on boards without much RAM we must ensure that we still leave
+     * enough room for a decent sized initrd, and on boards with large
+     * amounts of RAM we must avoid the initrd being so far up in RAM
+     * that it is outside lowmem and inaccessible to the kernel.
+     * So for boards with less  than 256MB of RAM we put the initrd
+     * halfway into RAM, and for boards with 256MB of RAM or more we put
+     * the initrd at 128MB.
+     */
+    info->initrd_start = info->loader_start +
+        MIN(info->ram_size / 2, 128 * 1024 * 1024);
+
     /* Assume that raw images are linux kernels, and ELF images are not.  */
     kernel_size = load_elf(info->kernel_filename, NULL, NULL, &elf_entry,
                            NULL, NULL, big_endian, ELF_MACHINE, 1);
@@ -398,10 +410,9 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info 
*info)
     if (is_linux) {
         if (info->initrd_filename) {
             initrd_size = load_image_targphys(info->initrd_filename,
-                                              info->loader_start
-                                              + INITRD_LOAD_ADDR,
-                                              info->ram_size
-                                              - INITRD_LOAD_ADDR);
+                                              info->initrd_start,
+                                              info->ram_size -
+                                              info->initrd_start);
             if (initrd_size < 0) {
                 fprintf(stderr, "qemu: could not load initrd '%s'\n",
                         info->initrd_filename);
@@ -419,9 +430,8 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info 
*info)
          */
         if (info->dtb_filename) {
             /* Place the DTB after the initrd in memory */
-            hwaddr dtb_start = TARGET_PAGE_ALIGN(info->loader_start
-                                                             + INITRD_LOAD_ADDR
-                                                             + initrd_size);
+            hwaddr dtb_start = TARGET_PAGE_ALIGN(info->initrd_start +
+                                                 initrd_size);
             if (load_dtb(dtb_start, info)) {
                 exit(1);
             }
-- 
1.7.9.5