[ARM] 3809/3: get rid of 4 megabyte kernel image size limit

We currently have a hardcoded 4 megabyte uncompressed kernel image
size limit, which is easily exceeded by, for example, enabling some of
the various kernel debugging options.

When setting up the initial page tables (which is where this 4M limit
is hardcoded), it's actually relatively easy to find out the true size
of the uncompressed kernel image and create enough page table entries
for things to fit, so this patch makes it so.

In the decompressor, we also need to know the size of the uncompressed
kernel image, to figure out whether there is any chance that uncompressing
the kernel might overwrite the compressed kernel image stored elsewhere
in memory. We don't have that info at this boot stage, though, so we
approximate the size of the uncompressed kernel by taking the compressed
kernel image size and allowing for a maximum 4x expansion.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

2 files changed, 11 insertions, 10 deletions

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index e5ab51b9cce..2568d311be2 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -237,7 +237,8 @@ not_relocated:	mov	r0, #0
  */
                 cmp     r4, r2
                 bhs     wont_overwrite
-                add     r0, r4, #4096*1024      @ 4MB largest kernel size
+                sub     r3, sp, r5              @ > compressed kernel size
+                add     r0, r4, r3, lsl #2      @ allow for 4x expansion
                 cmp     r0, r5
                 bls     wont_overwrite
 
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 5365d4e5949..ebc3e74a794 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -234,18 +234,18 @@ __create_page_tables:
 
         /*
          * Now setup the pagetables for our kernel direct
-         * mapped region.  We round TEXTADDR down to the
-         * nearest megabyte boundary.  It is assumed that
-         * the kernel fits within 4 contigous 1MB sections.
+         * mapped region.
          */
         add     r0, r4,  #(TEXTADDR & 0xff000000) >> 18 @ start of kernel
         str     r3, [r0, #(TEXTADDR & 0x00f00000) >> 18]!
-        add     r3, r3, #1 << 20
-        str     r3, [r0, #4]!                   @ KERNEL + 1MB
-        add     r3, r3, #1 << 20
-        str     r3, [r0, #4]!                   @ KERNEL + 2MB
-        add     r3, r3, #1 << 20
-        str     r3, [r0, #4]                    @ KERNEL + 3MB
+
+        ldr     r6, =(_end - PAGE_OFFSET - 1)   @ r6 = number of sections
+        mov     r6, r6, lsr #20                 @ needed for kernel minus 1
+
+1:      add     r3, r3, #1 << 20
+        str     r3, [r0, #4]!
+        subs    r6, r6, #1
+        bgt     1b
 
         /*
          * Then map first 1MB of ram in case it contains our boot params.