arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores

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@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210730112443.23245-16-will@kernel.org

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 583ee58..e0e7f4e 100644 (file)
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -469,15 +469,6 @@ 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);
-}
-
 static void update_sctlr_el1(u64 sctlr)
 {
        /*
@@ -519,7 +510,6 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
        ssbs_thread_switch(next);
        erratum_1418040_thread_switch(prev, next);
        ptrauth_thread_switch_user(next);
-       compat_thread_switch(next);
 
        /*
         * Complete any pending TLB or cache maintenance on this CPU in case
@@ -621,10 +611,8 @@ void arch_setup_new_exec(void)
                 * at the point of execve(), although we try a bit harder to
                 * honour the cpuset hierarchy.
                 */
-               if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
+               if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
                        force_compatible_cpus_allowed_ptr(current);
-                       set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
-               }
        } else if (static_branch_unlikely(&arm64_mismatched_32bit_el0)) {
                relax_compatible_cpus_allowed_ptr(current);
        }

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 2303633..22899c8 100644 (file)
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -912,19 +912,6 @@ 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)
 {
@@ -952,19 +939,6 @@ 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)