arm64: ptdump: Don't override the level when operating on the stage-2 tables

Ptdump uses the init_mm structure directly to dump the kernel
pagetables. When ptdump is called on the stage-2 pagetables, this mm
argument is not used. Prevent the level from being overwritten by
checking the argument against NULL.
Signed-off-by: Sebastian Ene <sebastianene@google.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20240909124721.1672199-5-sebastianene@google.comSigned-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/mm/ptdump.c

@@ -197,8 +197,8 @@ void note_page(struct ptdump_state *pt_st, unsigned long addr, int level,
 	u64 prot = 0;
 
 	/* check if the current level has been folded dynamically */
-	if ((level == 1 && mm_p4d_folded(st->mm)) ||
-	    (level == 2 && mm_pud_folded(st->mm)))
+	if (st->mm && ((level == 1 && mm_p4d_folded(st->mm)) ||
+	    (level == 2 && mm_pud_folded(st->mm))))
 		level = 0;
 
 	if (level >= 0)