efi/libstub: arm32: Base FDT and initrd placement on image address

The way we use the base of DRAM in the EFI stub is problematic as it
is ill defined what the base of DRAM actually means. There are some
restrictions on the placement of FDT and initrd which are defined in
terms of dram_base, but given that the placement of the kernel in
memory is what defines these boundaries (as on ARM, this is where the
linear region starts), it is better to use the image address in these
cases, and disregard dram_base altogether.

Reviewed-by: Maxim Uvarov <maxim.uvarov@linaro.org>
Tested-by: Maxim Uvarov <maxim.uvarov@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

1 files changed, 11 insertions, 12 deletions

diff --git a/arch/arm/include/asm/efi.h b/arch/arm/include/asm/efi.h
index 5dcf3c6011b7..3ee4f4381985 100644
--- a/arch/arm/include/asm/efi.h
+++ b/arch/arm/include/asm/efi.h
@@ -66,25 +66,24 @@ static inline void efifb_setup_from_dmi(struct screen_info *si, const char *opt)
 #define MAX_UNCOMP_KERNEL_SIZE	SZ_32M
 
 /*
- * The kernel zImage should preferably be located between 32 MB and 128 MB
- * from the base of DRAM. The min address leaves space for a maximal size
- * uncompressed image, and the max address is due to how the zImage decompressor
- * picks a destination address.
+ * phys-to-virt patching requires that the physical to virtual offset fits
+ * into the immediate field of an add/sub instruction, which comes down to the
+ * 24 least significant bits being zero, and so the offset should be a multiple
+ * of 16 MB. Since PAGE_OFFSET itself is a multiple of 16 MB, the physical
+ * base should be aligned to 16 MB as well.
  */
-#define ZIMAGE_OFFSET_LIMIT	SZ_128M
-#define MIN_ZIMAGE_OFFSET	MAX_UNCOMP_KERNEL_SIZE
+#define EFI_PHYS_ALIGN		SZ_16M
 
-/* on ARM, the FDT should be located in the first 128 MB of RAM */
-static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
+/* on ARM, the FDT should be located in a lowmem region */
+static inline unsigned long efi_get_max_fdt_addr(unsigned long image_addr)
 {
-	return dram_base + ZIMAGE_OFFSET_LIMIT;
+	return round_down(image_addr, EFI_PHYS_ALIGN) + SZ_512M;
 }
 
 /* on ARM, the initrd should be loaded in a lowmem region */
-static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
-						    unsigned long image_addr)
+static inline unsigned long efi_get_max_initrd_addr(unsigned long image_addr)
 {
-	return dram_base + SZ_512M;
+	return round_down(image_addr, EFI_PHYS_ALIGN) + SZ_512M;
 }
 
 struct efi_arm_entry_state {