[PATCH v4 14/14] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores

[Will Deacon]

The scheduler now knows enough about these braindead systems to place
32-bit tasks accordingly, so throw out the safety checks and allow the
ret-to-user path to avoid do_notify_resume() if there is nothing to do.

Signed-off-by: Will Deacon <will at kernel.org>
---
 arch/arm64/kernel/process.c | 14 +-------------
 arch/arm64/kernel/signal.c  | 26 --------------------------
 2 files changed, 1 insertion(+), 39 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 72116b0c7c73..e21c631c8b17 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -543,15 +543,6 @@ 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 (static_branch_unlikely(&arm64_mismatched_32bit_el0))
-		set_tsk_thread_flag(next, TIF_NOTIFY_RESUME);
-}
-
 /*
  * Thread switching.
  */
@@ -568,7 +559,6 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	uao_thread_switch(next);
 	ssbs_thread_switch(next);
 	erratum_1418040_thread_switch(prev, next);
-	compat_thread_switch(next);
 
 	/*
 	 * Complete any pending TLB or cache maintenance on this CPU in case
@@ -644,7 +634,7 @@ static void adjust_compat_task_affinity(struct task_struct *p)
 	 * execve().
 	 */
 	if (!restrict_cpus_allowed_ptr(p, possible_mask))
-		goto out;
+		return;
 
 	if (alloc_cpumask_var(&cpuset_mask, GFP_KERNEL)) {
 		cpuset_cpus_allowed(p, cpuset_mask);
@@ -661,8 +651,6 @@ static void adjust_compat_task_affinity(struct task_struct *p)
 out_set_mask:
 	set_cpus_allowed_ptr(p, newmask);
 	free_cpumask_var(cpuset_mask);
-out:
-	set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
 }
 
 /*
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index bcb6ca2d9a7c..a8184cad8890 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -911,19 +911,6 @@ static void do_signal(struct pt_regs *regs)
 	restore_saved_sigmask();
 }
 
-static bool cpu_affinity_invalid(struct pt_regs *regs)
-{
-	if (!compat_user_mode(regs))
-		return false;
-
-	/*
-	 * We're preemptible, but a reschedule will cause us to check the
-	 * affinity again.
-	 */
-	return !cpumask_test_cpu(raw_smp_processor_id(),
-				 system_32bit_el0_cpumask());
-}
-
 asmlinkage void do_notify_resume(struct pt_regs *regs,
 				 unsigned long thread_flags)
 {
@@ -961,19 +948,6 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 			if (thread_flags & _TIF_NOTIFY_RESUME) {
 				tracehook_notify_resume(regs);
 				rseq_handle_notify_resume(NULL, regs);
-
-				/*
-				 * If we reschedule after checking the affinity
-				 * then we must ensure that TIF_NOTIFY_RESUME
-				 * is set so that we check the affinity again.
-				 * Since tracehook_notify_resume() clears the
-				 * flag, ensure that the compiler doesn't move
-				 * it after the affinity check.
-				 */
-				barrier();
-
-				if (cpu_affinity_invalid(regs))
-					force_sig(SIGKILL);
 			}
 
 			if (thread_flags & _TIF_FOREIGN_FPSTATE)
-- 
2.29.2.454.gaff20da3a2-goog