arm64: mm: move vmemmap region right below the linear region
This moves the vmemmap region right below PAGE_OFFSET, aka the start
of the linear region, and redefines its size to be a power of two.
Due to the placement of PAGE_OFFSET in the middle of the address space,
whose size is a power of two as well, this guarantees that virt to
page conversions and vice versa can be implemented efficiently, by
masking and shifting rather than ordinary arithmetic.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 377257a..2abfa4d 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -24,20 +24,15 @@
#include <asm/pgtable-prot.h>
/*
- * VMALLOC and SPARSEMEM_VMEMMAP ranges.
+ * VMALLOC range.
*
- * VMEMAP_SIZE: allows the whole linear region to be covered by a struct page array
- * (rounded up to PUD_SIZE).
* VMALLOC_START: beginning of the kernel vmalloc space
- * VMALLOC_END: extends to the available space below vmmemmap, PCI I/O space,
- * fixed mappings and modules
+ * VMALLOC_END: extends to the available space below vmmemmap, PCI I/O space
+ * and fixed mappings
*/
-#define VMEMMAP_SIZE ALIGN((1UL << (VA_BITS - PAGE_SHIFT - 1)) * sizeof(struct page), PUD_SIZE)
-
#define VMALLOC_START (MODULES_END)
#define VMALLOC_END (PAGE_OFFSET - PUD_SIZE - VMEMMAP_SIZE - SZ_64K)
-#define VMEMMAP_START (VMALLOC_END + SZ_64K)
#define vmemmap ((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
#define FIRST_USER_ADDRESS 0UL