From: Steve Capper <steve.capper@arm.com>
Date: Wed, 7 Aug 2019 16:55:21 +0100
Subject: arm64: mm: Modify calculation of VMEMMAP_SIZE
Patch-mainline: v5.4-rc1
Git-commit: ce3aaed87344c83c77135f80e7b76e1da9c92ee6
References: jsc#SLE-16407

In a later patch we will need to have a slightly larger VMEMMAP region
to accommodate boot time selection between 48/52-bit kernel VAs.

This patch modifies the formula for computing VMEMMAP_SIZE to depend
explicitly on the PAGE_OFFSET and start of kernel addressable memory.
(This allows for a slightly larger direct linear map in future).

Signed-off-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Acked-by: Lee, Chun-Yi <jlee@suse.com>
---
 arch/arm64/include/asm/memory.h |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -26,8 +26,15 @@
 /*
  * VMEMMAP_SIZE - allows the whole linear region to be covered by
  *                a struct page array
+ *
+ * If we are configured with a 52-bit kernel VA then our VMEMMAP_SIZE
+ * neads to cover the memory region from the beginning of the 52-bit
+ * PAGE_OFFSET all the way to VA_START for 48-bit. This allows us to
+ * keep a constant PAGE_OFFSET and "fallback" to using the higher end
+ * of the VMEMMAP where 52-bit support is not available in hardware.
  */
-#define VMEMMAP_SIZE (UL(1) << (VA_BITS - PAGE_SHIFT - 1 + STRUCT_PAGE_MAX_SHIFT))
+#define VMEMMAP_SIZE ((_VA_START(VA_BITS_MIN) - PAGE_OFFSET) \
+			>> (PAGE_SHIFT - STRUCT_PAGE_MAX_SHIFT))
 
 /*
  * PAGE_OFFSET - the virtual address of the start of the linear map (top