powerpc/mm/radix: Fix small page at boundary when splitting

When we have CONFIG_STRICT_KERNEL_RWX enabled, we want to split the
linear mapping at the text/data boundary so we can map the kernel
text read only.

Currently we always use a small page at the text/data boundary, even
when that's not necessary:

  Mapped 0x0000000000000000-0x0000000000e00000 with 2.00 MiB pages
  Mapped 0x0000000000e00000-0x0000000001000000 with 64.0 KiB pages
  Mapped 0x0000000001000000-0x0000000040000000 with 2.00 MiB pages

This is because the check that the mapping crosses the __init_begin
boundary is too strict, it also returns true when we map exactly up to
the boundary.

So fix it to check that the mapping would actually map past
__init_begin, and with that we see:

  Mapped 0x0000000000000000-0x0000000040000000 with 2.00 MiB pages
  Mapped 0x0000000040000000-0x0000000100000000 with 1.00 GiB pages

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/pgtable-radix.c

@@ -295,14 +295,14 @@ retry:
 
 		if (split_text_mapping && (mapping_size == PUD_SIZE) &&
 			(addr < __pa_symbol(__init_begin)) &&
-			(addr + mapping_size) >= __pa_symbol(__init_begin)) {
+			(addr + mapping_size) > __pa_symbol(__init_begin)) {
 			max_mapping_size = PMD_SIZE;
 			goto retry;
 		}
 
 		if (split_text_mapping && (mapping_size == PMD_SIZE) &&
 		    (addr < __pa_symbol(__init_begin)) &&
-		    (addr + mapping_size) >= __pa_symbol(__init_begin)) {
+		    (addr + mapping_size) > __pa_symbol(__init_begin)) {
 			mapping_size = PAGE_SIZE;
 			psize = mmu_virtual_psize;
 		}