arm64: mte: Save/Restore TFSR_EL1 during suspend

When MTE async mode is enabled TFSR_EL1 contains the accumulative
asynchronous tag check faults for EL1 and EL0.

During the suspend/resume operations the firmware might perform some
operations that could change the state of the register resulting in
a spurious tag check fault report.

Save/restore the state of the TFSR_EL1 register during the
suspend/resume operations to prevent this to happen.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

arch/arm64/include/asm/mte.h

@@ -43,6 +43,7 @@ void mte_sync_tags(pte_t *ptep, pte_t pte);
 void mte_copy_page_tags(void *kto, const void *kfrom);
 void flush_mte_state(void);
 void mte_thread_switch(struct task_struct *next);
+void mte_suspend_enter(void);
 void mte_suspend_exit(void);
 long set_mte_ctrl(struct task_struct *task, unsigned long arg);
 long get_mte_ctrl(struct task_struct *task);
@@ -68,6 +69,9 @@ static inline void flush_mte_state(void)
 static inline void mte_thread_switch(struct task_struct *next)
 {
 }
+static inline void mte_suspend_enter(void)
+{
+}
 static inline void mte_suspend_exit(void)
 {
 }

arch/arm64/kernel/mte.c

@@ -25,6 +25,7 @@
 
 u64 gcr_kernel_excl __ro_after_init;
 
+static u64 mte_suspend_tfsr_el1;
 static bool report_fault_once = true;
 
 /* Whether the MTE asynchronous mode is enabled. */
@@ -295,12 +296,33 @@ void mte_thread_switch(struct task_struct *next)
 	mte_check_tfsr_el1();
 }
 
+void mte_suspend_enter(void)
+{
+	if (!system_supports_mte())
+		return;
+
+	/*
+	 * The barriers are required to guarantee that the indirect writes
+	 * to TFSR_EL1 are synchronized before we save the state.
+	 */
+	dsb(nsh);
+	isb();
+
+	/* Save SYS_TFSR_EL1 before suspend entry */
+	mte_suspend_tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);
+}
+
 void mte_suspend_exit(void)
 {
 	if (!system_supports_mte())
 		return;
 
 	update_gcr_el1_excl(gcr_kernel_excl);
+
+	/* Resume SYS_TFSR_EL1 after suspend exit */
+	write_sysreg_s(mte_suspend_tfsr_el1, SYS_TFSR_EL1);
+
+	mte_check_tfsr_el1();
 }
 
 long set_mte_ctrl(struct task_struct *task, unsigned long arg)

arch/arm64/kernel/suspend.c

@@ -91,6 +91,9 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 	unsigned long flags;
 	struct sleep_stack_data state;
 
+	/* Report any MTE async fault before going to suspend. */
+	mte_suspend_enter();
+
 	/*
 	 * From this point debug exceptions are disabled to prevent
 	 * updates to mdscr register (saved and restored along with