ARM: 7751/1: zImage: don't overwrite ourself with a page table

When zImage is loaded into RAM at a low address but TEXT_OFFSET
is set higher, we risk overwriting ourself with the page table
needed to turn on the cache as it is located relative to the relocation
address.  Let's defer the cache setup after relocation in that case.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Reported-by: Stephen Boyd <sboyd@codeurora.org>
Tested-by: Stephen Boyd <sboyd@codeurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index fe4d9c3ad761c8dfaadce6e214d709417947f396..8e0d0ada62dfef4fc8dd2f2c398e27956467d8e0 100644 (file)
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -182,7 +182,19 @@ not_angel:
                ldr     r4, =zreladdr
 #endif
 
-               bl      cache_on
+               /*
+                * Set up a page table only if it won't overwrite ourself.
+                * That means r4 < pc && r4 - 16k page directory > &_end.
+                * Given that r4 > &_end is most unfrequent, we add a rough
+                * additional 1MB of room for a possible appended DTB.
+                */
+               mov     r0, pc
+               cmp     r0, r4
+               ldrcc   r0, LC0+32
+               addcc   r0, r0, pc
+               cmpcc   r4, r0
+               orrcc   r4, r4, #1              @ remember we skipped cache_on
+               blcs    cache_on
 
 restart:       adr     r0, LC0
                ldmia   r0, {r1, r2, r3, r6, r10, r11, r12}
@@ -228,7 +240,7 @@ restart:    adr     r0, LC0
  *   r0  = delta
  *   r2  = BSS start
  *   r3  = BSS end
- *   r4  = final kernel address
+ *   r4  = final kernel address (possibly with LSB set)
  *   r5  = appended dtb size (still unknown)
  *   r6  = _edata
  *   r7  = architecture ID
@@ -276,6 +288,7 @@ restart:    adr     r0, LC0
                 */
                cmp     r0, #1
                sub     r0, r4, #TEXT_OFFSET
+               bic     r0, r0, #1
                add     r0, r0, #0x100
                mov     r1, r6
                sub     r2, sp, r6
@@ -322,12 +335,13 @@ dtb_check_done:
 
 /*
  * Check to see if we will overwrite ourselves.
- *   r4  = final kernel address
+ *   r4  = final kernel address (possibly with LSB set)
  *   r9  = size of decompressed image
  *   r10 = end of this image, including  bss/stack/malloc space if non XIP
  * We basically want:
  *   r4 - 16k page directory >= r10 -> OK
  *   r4 + image length <= address of wont_overwrite -> OK
+ * Note: the possible LSB in r4 is harmless here.
  */
                add     r10, r10, #16384
                cmp     r4, r10
@@ -389,7 +403,8 @@ dtb_check_done:
                add     sp, sp, r6
 #endif
 
-               bl      cache_clean_flush
+               tst     r4, #1
+               bleq    cache_clean_flush
 
                adr     r0, BSYM(restart)
                add     r0, r0, r6
@@ -401,7 +416,7 @@ wont_overwrite:
  *   r0  = delta
  *   r2  = BSS start
  *   r3  = BSS end
- *   r4  = kernel execution address
+ *   r4  = kernel execution address (possibly with LSB set)
  *   r5  = appended dtb size (0 if not present)
  *   r7  = architecture ID
  *   r8  = atags pointer
@@ -464,6 +479,15 @@ not_relocated:     mov     r0, #0
                cmp     r2, r3
                blo     1b
 
+               /*
+                * Did we skip the cache setup earlier?
+                * That is indicated by the LSB in r4.
+                * Do it now if so.
+                */
+               tst     r4, #1
+               bic     r4, r4, #1
+               blne    cache_on
+
 /*
  * The C runtime environment should now be setup sufficiently.
  * Set up some pointers, and start decompressing.
@@ -512,6 +536,7 @@ LC0:                .word   LC0                     @ r1
                .word   _got_start              @ r11
                .word   _got_end                @ ip
                .word   .L_user_stack_end       @ sp
+               .word   _end - restart + 16384 + 1024*1024
                .size   LC0, . - LC0
 
 #ifdef CONFIG_ARCH_RPC