[PATCH 2/2] arm64/mm: Avoid ID mapping of kpti flag if it is no longer needed

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb at kernel.org>

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 at kernel.org>
---
 arch/arm64/mm/mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index b131ed31a6c8..bf5b1c426ad0 100644
--- 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);
 
-- 
2.44.0.278.ge034bb2e1d-goog