powerpc/code-patching: Avoid r/w mapping of the zero page

The only remaining use of map_patch_area() is mapping the zero page, and
immediately unmapping it again so that the intermediate page table
levels are all guaranteed to be populated.

The use of the zero page here is completely arbitrary, and not harmful
per se, but currently, it creates a writable mapping, and does so in a
manner that requires that the empty_zero_page[] symbol is not
const-qualified.

Given that this is about to change, and that map_patch_area() now never
maps anything other than the zero page, let's simplify the code and
- remove the helpers and call [un]map_kernel_page() directly
- take the PA of empty_zero_page directly
- create a read-only temporary mapping.

This allows empty_zero_page[] to be repainted as const u8[] in a
subsequent patch, without making substantial changes to this code
patching logic.

Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Link: https://lore.kernel.org/all/20260520085423.485402-1-ardb@kernel.org/
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

0 files changed, 0 insertions, 0 deletions