Merge "arm64: SW PAN: Point saved ttbr0 at the zero page when switching to init_mm"

arch/arm64/include/asm/efi.h

@@ -87,10 +87,8 @@ static inline void efi_set_pgd(struct mm_struct *mm)
 			 * Defer the switch to the current thread's TTBR0_EL1
 			 * until uaccess_enable(). Restore the current
 			 * thread's saved ttbr0 corresponding to its active_mm
-			 * (if different from init_mm).
 			 */
 			cpu_set_reserved_ttbr0();
-			if (current->active_mm != &init_mm)
 			update_saved_ttbr0(current, current->active_mm);
 		}
 	}

arch/arm64/include/asm/mmu_context.h

@@ -183,11 +183,17 @@ enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
 static inline void update_saved_ttbr0(struct task_struct *tsk,
 				      struct mm_struct *mm)
 {
-	if (system_uses_ttbr0_pan()) {
+	u64 ttbr;
-		BUG_ON(mm->pgd == swapper_pg_dir);
+
-		task_thread_info(tsk)->ttbr0 =
+	if (!system_uses_ttbr0_pan())
-			virt_to_phys(mm->pgd) | ASID(mm) << 48;
+		return;
-	}
+
+	if (mm == &init_mm)
+		ttbr = __pa_symbol(empty_zero_page);
+	else
+		ttbr = virt_to_phys(mm->pgd) | ASID(mm) << 48;
+
+	task_thread_info(tsk)->ttbr0 = ttbr;
 }
 #else
 static inline void update_saved_ttbr0(struct task_struct *tsk,
@@ -223,10 +229,8 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	 * Update the saved TTBR0_EL1 of the scheduled-in task as the previous
 	 * value may have not been initialised yet (activate_mm caller) or the
 	 * ASID has changed since the last run (following the context switch
-	 * of another thread of the same process). Avoid setting the reserved
+	 * of another thread of the same process).
-	 * TTBR0_EL1 to swapper_pg_dir (init_mm; e.g. via idle_task_exit).
 	 */
-	if (next != &init_mm)
 	update_saved_ttbr0(tsk, next);
 }