On Wed, Oct 28, 2020 at 12:10:53PM +0000, Catalin Marinas wrote:

On Tue, Oct 27, 2020 at 09:51:16PM +0000, Will Deacon wrote:

quoted

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 4784011cecac..c45b5f9dd66b 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c

@@ -542,6 +542,17 @@ static void erratum_1418040_thread_switch(struct task_struct *prev,
 	write_sysreg(val, cntkctl_el1);
 }
 
+static void compat_thread_switch(struct task_struct *next)
+{
+	if (!is_compat_thread(task_thread_info(next)))
+		return;
+
+	if (!system_has_mismatched_32bit_el0())
+		return;
+
+	set_tsk_thread_flag(next, TIF_NOTIFY_RESUME);
+}

I wonder whether you could use set_notify_resume() for consistency.

I looked at that, but it ends up kicking the task which is not needed
here and can result in a reschedule via preempt_enable().

Will

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