arm64: mm: Only map KPTI trampoline if it is going to be used

Avoid creating the fixmap entries for the KPTI trampoline if KPTI is not
in use.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20231127120049.2258650-7-ardb@google.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: ardbiesheuvel

arch/arm64/mm/mmu.c

@@ -674,6 +674,9 @@ static int __init map_entry_trampoline(void)
 {
 	int i;
 
+	if (!arm64_kernel_unmapped_at_el0())
+		return 0;
+
 	pgprot_t prot = kernel_exec_prot();
 	phys_addr_t pa_start = __pa_symbol(__entry_tramp_text_start);