From adb58517418007dada1f7f98ff222b26b0c3b4c2 Mon Sep 17 00:00:00 2001
From: Valentin Schneider <valentin.schneider@arm.com>
Date: Wed, 11 Aug 2021 21:13:54 +0100
Subject: [PATCH 003/158] arm64: mm: Make arch_faults_on_old_pte() check for
 migratability

arch_faults_on_old_pte() relies on the calling context being
non-preemptible. CONFIG_PREEMPT_RT turns the PTE lock into a sleepable
spinlock, which doesn't disable preemption once acquired, triggering the
warning in arch_faults_on_old_pte().

It does however disable migration, ensuring the task remains on the same
CPU during the entirety of the critical section, making the read of
cpu_has_hw_af() safe and stable.

Make arch_faults_on_old_pte() check migratable() instead of preemptible().

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20210811201354.1976839-5-valentin.schneider@arm.com
---
 arch/arm64/include/asm/pgtable.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-5.15.19-rt29/arch/arm64/include/asm/pgtable.h
===================================================================
--- linux-5.15.19-rt29.orig/arch/arm64/include/asm/pgtable.h
+++ linux-5.15.19-rt29/arch/arm64/include/asm/pgtable.h
@@ -1001,7 +1001,7 @@ static inline void update_mmu_cache(stru
  */
 static inline bool arch_faults_on_old_pte(void)
 {
-	WARN_ON(preemptible());
+	WARN_ON(is_migratable());
 
 	return !cpu_has_hw_af();
 }