@@ -263,6 +263,39 @@ SYM_FUNC_END(clear_page_tables)
populate_entries \tbl, \rtbl, \istart, \iend, \flags, #SWAPPER_BLOCK_SIZE, \tmp
.endm
+/*
+ * Remap a subregion created with the map_memory macro with modified attributes
+ * or output address. The entire remapped region must have been covered in the
+ * invocation of map_memory.
+ *
+ * x0: last level table address (returned in first argument to map_memory)
+ * x1: start VA of the existing mapping
+ * x2: start VA of the region to update
+ * x3: end VA of the region to update (exclusive)
+ * x4: start PA associated with the region to update
+ * x5: attributes to set on the updated region
+ * x6: order of the last level mappings
+ */
+SYM_FUNC_START_LOCAL(remap_region)
+ sub x3, x3, #1 // make end inclusive
+
+ // Get the index offset for the start of the last level table
+ lsr x1, x1, x6
+ bfi x1, xzr, #0, #PAGE_SHIFT - 3
+
+ // Derive the start and end indexes into the last level table
+ // associated with the provided region
+ lsr x2, x2, x6
+ lsr x3, x3, x6
+ sub x2, x2, x1
+ sub x3, x3, x1
+
+ mov x1, #1
+ lsl x6, x1, x6 // block size at this level
+
+ populate_entries x0, x4, x2, x3, x5, x6, x7
+ ret
+SYM_FUNC_END(remap_region)
SYM_FUNC_START_LOCAL(create_idmap)
adrp x0, idmap_pg_dir
The asm macros used to create the initial ID map and kernel mappings don't support randomly remapping parts of the address space after it has been populated. What we can do, however, given that all block or page mappings are created at the final level, is take a subset of the mapped range and update its attributes or output address. This will permit us to make parts of these page tables read-only, or remap a part of it to cover the device tree. So add a helper that encapsulates this. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- arch/arm64/kernel/head.S | 33 ++++++++++++++++++++ 1 file changed, 33 insertions(+)