[PATCH v5 11/13] arm64: mm: Don't abuse memblock NOMAP to check for overlaps

[Ard Biesheuvel <ardb+git@google.com>]

From: Ard Biesheuvel <ardb@kernel.org>

Now that the DRAM mapping routines respect existing table mappings and
contiguous block and page mappings, it is no longer needed to fiddle
with the memblock tables to set and clear the NOMAP attribute in order
to omit text and rodata when creating the linear map.

Instead, map the kernel text and rodata alias first with the desired
attributes, so that they will not be remapped later with different
attributes when mapping the memblocks.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/mm/mmu.c | 24 +++++++-------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index d4ad9e4766a6..dcff1a538f20 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1148,12 +1148,15 @@ static void __init map_mem(void)
 		flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
 
 	/*
-	 * Take care not to create a writable alias for the
-	 * read-only text and rodata sections of the kernel image.
-	 * So temporarily mark them as NOMAP to skip mappings in
-	 * the following for-loop
+	 * Map the linear alias of the [_text, __init_begin) interval
+	 * as non-executable now, and remove the write permission in
+	 * mark_linear_text_alias_ro() above (which will be called after
+	 * alternative patching has completed). This makes the contents
+	 * of the region accessible to subsystems such as hibernate,
+	 * but protects it from inadvertent modification or execution.
 	 */
-	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
+	__map_memblock(kernel_start, kernel_end, pgprot_tagged(PAGE_KERNEL),
+		       flags);
 
 	/* map all the memory banks */
 	for_each_mem_range(i, &start, &end) {
@@ -1165,17 +1168,6 @@ static void __init map_mem(void)
 		__map_memblock(start, end, pgprot_tagged(PAGE_KERNEL),
 			       flags);
 	}
-
-	/*
-	 * Map the linear alias of the [_text, __init_begin) interval
-	 * as non-executable now, and remove the write permission in
-	 * mark_linear_text_alias_ro() below (which will be called after
-	 * alternative patching has completed). This makes the contents
-	 * of the region accessible to subsystems such as hibernate,
-	 * but protects it from inadvertent modification or execution.
-	 */
-	__map_memblock(kernel_start, kernel_end, pgprot_tagged(PAGE_KERNEL), 0);
-	memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
 }
 
 void mark_rodata_ro(void)
-- 
2.54.0.563.g4f69b47b94-goog