[PATCH v3 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0

[Will Deacon <will@xxxxxxxxxx>]

When exec'ing a 32-bit task on a system with mismatched support for
32-bit EL0, try to ensure that it starts life on a CPU that can actually
run it.

Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
 arch/arm64/kernel/process.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 1540ab0fbf23..17b94007fed4 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -625,6 +625,16 @@ unsigned long arch_align_stack(unsigned long sp)
 	return sp & ~0xf;
 }
 
+static void adjust_compat_task_affinity(struct task_struct *p)
+{
+	const struct cpumask *mask = system_32bit_el0_cpumask();
+
+	if (restrict_cpus_allowed_ptr(p, mask))
+		set_cpus_allowed_ptr(p, mask);
+
+	set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+}
+
 /*
  * Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
  */
@@ -635,7 +645,7 @@ void arch_setup_new_exec(void)
 	if (is_compat_task()) {
 		mmflags = MMCF_AARCH32;
 		if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
-			set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+			adjust_compat_task_affinity(current);
 	}
 
 	current->mm->context.flags = mmflags;
-- 
2.29.2.299.gdc1121823c-goog