arm64: mm: allocate pagetables anywhere

Now that create_mapping uses fixmap slots to modify pte, pmd, and pud
entries, we can access page tables anywhere in physical memory,
regardless of the extent of the linear mapping.

Given that, we no longer need to limit memblock allocations during page
table creation, and can leave the limit as its default
MEMBLOCK_ALLOC_ANYWHERE.

We never add memory which will fall outside of the linear map range
given phys_offset and MAX_MEMBLOCK_ADDR are configured appropriately, so
any tables we create will fall in the linear map of the final tables.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Cc: Laura Abbott <labbott@fedoraproject.org>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/mmu.c

@@ -384,20 +384,6 @@ static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 static void __init map_mem(void)
 {
 	struct memblock_region *reg;
-	phys_addr_t limit;
-
-	/*
-	 * Temporarily limit the memblock range. We need to do this as
-	 * create_mapping requires puds, pmds and ptes to be allocated from
-	 * memory addressable from the initial direct kernel mapping.
-	 *
-	 * The initial direct kernel mapping, located at swapper_pg_dir, gives
-	 * us PUD_SIZE (with SECTION maps) or PMD_SIZE (without SECTION maps,
-	 * memory starting from PHYS_OFFSET (which must be aligned to 2MB as
-	 * per Documentation/arm64/booting.txt).
-	 */
-	limit = PHYS_OFFSET + SWAPPER_INIT_MAP_SIZE;
-	memblock_set_current_limit(limit);
 
 	/* map all the memory banks */
 	for_each_memblock(memory, reg) {
@@ -409,29 +395,8 @@ static void __init map_mem(void)
 		if (memblock_is_nomap(reg))
 			continue;
 
-		if (ARM64_SWAPPER_USES_SECTION_MAPS) {
-			/*
-			 * For the first memory bank align the start address and
-			 * current memblock limit to prevent create_mapping() from
-			 * allocating pte page tables from unmapped memory. With
-			 * the section maps, if the first block doesn't end on section
-			 * size boundary, create_mapping() will try to allocate a pte
-			 * page, which may be returned from an unmapped area.
-			 * When section maps are not used, the pte page table for the
-			 * current limit is already present in swapper_pg_dir.
-			 */
-			if (start < limit)
-				start = ALIGN(start, SECTION_SIZE);
-			if (end < limit) {
-				limit = end & SECTION_MASK;
-				memblock_set_current_limit(limit);
-			}
-		}
 		__map_memblock(start, end);
 	}
-
-	/* Limit no longer required. */
-	memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE);
 }
 
 static void __init fixup_executable(void)