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    Subject[PATCH v3 14/14] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores
    Date
    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>
    ---
    arch/arm64/kernel/process.c | 12 ------------
    arch/arm64/kernel/signal.c | 26 --------------------------
    2 files changed, 38 deletions(-)

    diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
    index 17b94007fed4..dba94af1b840 100644
    --- a/arch/arm64/kernel/process.c
    +++ b/arch/arm64/kernel/process.c
    @@ -542,15 +542,6 @@ 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.
    */
    @@ -567,7 +558,6 @@ __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
    @@ -631,8 +621,6 @@ static void adjust_compat_task_affinity(struct task_struct *p)

    if (restrict_cpus_allowed_ptr(p, mask))
    set_cpus_allowed_ptr(p, mask);
    -
    - 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)
    --
    2.29.2.299.gdc1121823c-goog
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