arm64/mm: Avoid ID mapping of kpti flag if it is no longer needed

arm64_use_ng_mappings will be set to 'true' by the early boot code if it
decides to use non-global (nG) attributes for all kernel mappings,
typically when enabling KASLR on a system that does not implement E0PD.

In this case, the G-to-nG update routines are never called, and so there
is no reason to create the writable mapping of the associated status
flag in the ID map.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240301104046.1234309-6-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index b131ed31a6c8420c582b25c9eb844dadb3d2ce70..bf5b1c426ad0dd8137968f9484d90ae2e757d9f3 100644 (file)
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -777,7 +777,7 @@ static void __init create_idmap(void)
                       IDMAP_ROOT_LEVEL, (pte_t *)idmap_pg_dir, false,
                       __phys_to_virt(ptep) - ptep);
 
-       if (IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0)) {
+       if (IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0) && !arm64_use_ng_mappings) {
                extern u32 __idmap_kpti_flag;
                u64 pa = __pa_symbol(&__idmap_kpti_flag);