Re: [PATCH v13 6/7] arm64: mte: Report async tag faults before suspend

On Fri, Feb 12, 2021 at 12:00:15PM +0000, Lorenzo Pieralisi wrote:

On Thu, Feb 11, 2021 at 03:33:52PM +0000, Vincenzo Frascino wrote:

quoted

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.

Report asynchronous tag faults before suspend and clear the TFSR_EL1
register after resume to prevent this to happen.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Lorenzo Pieralisi <redacted>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
---
 arch/arm64/include/asm/mte.h |  4 ++++
 arch/arm64/kernel/mte.c      | 20 ++++++++++++++++++++
 arch/arm64/kernel/suspend.c  |  3 +++
 3 files changed, 27 insertions(+)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 43169b978cd3..33e88a470357 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h

@@ -41,6 +41,7 @@ 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);

@@ -66,6 +67,9 @@ 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)
 {
 }

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index f5aa5bea6dfe..de905102245a 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c

@@ -258,12 +258,32 @@ 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 report the state.
+	 */
+	dsb(nsh);
+	isb();
+
+	/* Report SYS_TFSR_EL1 before suspend entry */
+	mte_check_tfsr_el1();
+}
+
 void mte_suspend_exit(void)
 {
 	if (!system_supports_mte())
 		return;
 
 	update_gcr_el1_excl(gcr_kernel_excl);
+
+	/* Clear SYS_TFSR_EL1 after suspend exit */
+	write_sysreg_s(0, SYS_TFSR_EL1);

AFAICS it is not needed, it is done already in __cpu_setup() (that is
called by cpu_resume on return from cpu_suspend() from firmware).

However, I have a question. We are relying on context switch to set
sctlr_el1_tfc0 right ? If that's the case, till the thread resuming from
low power switches context we are running with SCTLR_EL1_TCF0 not
reflecting the actual value.

Forget this, we obviously restore sctlr_el1 on resume (cpu_do_resume()).

With the line above removed:

Reviewed-by: Lorenzo Pieralisi <redacted>

Just making sure that I understand it correctly, I need to check the
resume from suspend-to-RAM path, it is something that came up with perf
save/restore already in the past.

Lorenzo

quoted

+
 }
 
 long set_mte_ctrl(struct task_struct *task, unsigned long arg)

diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
index a67b37a7a47e..25a02926ad88 100644
--- a/arch/arm64/kernel/suspend.c
+++ b/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

-- 
2.30.0

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