linux-kernel - Re: [PATCH] LoongArch: Fix irq enable in exception handlers

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Date:   Tue, 27 Dec 2022 15:37:02 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Jinyang He <hejinyang@...ngson.cn>
Cc:     WANG Xuerui <kernel@...0n.name>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Fix irq enable in exception handlers

Hi, Jinyang,

Move die_if_kernel to irq disabled context to solve what? And LBT is
surely allowed to be triggered in kernel context.

Huacai

On Wed, Dec 21, 2022 at 3:43 PM Jinyang He <hejinyang@...ngson.cn> wrote:
>
> The interrupt state can be got by regs->csr_prmd. Once previous
> interrupt state is disable, we shouldn't enable interrupt if we
> triggered exception which can be triggered in kernel mode. So
> conditionally enable interrupt. For those do_\exception which
> can not triggered in kernel mode but need enable interrupt, call
> die_if_kernel() firstly. And for do_lsx, do_lasx and do_lbt cannot
> triggered in kernel mode, too.
>
> Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
> ---
>  arch/loongarch/kernel/traps.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
> index 1ea14f6c18d3..3ac7b32d1e15 100644
> --- a/arch/loongarch/kernel/traps.c
> +++ b/arch/loongarch/kernel/traps.c
> @@ -340,9 +340,9 @@ asmlinkage void noinstr do_fpe(struct pt_regs *regs, unsigned long fcsr)
>
>         /* Clear FCSR.Cause before enabling interrupts */
>         write_fcsr(LOONGARCH_FCSR0, fcsr & ~mask_fcsr_x(fcsr));
> -       local_irq_enable();
>
>         die_if_kernel("FP exception in kernel code", regs);
> +       local_irq_enable();
>
>         sig = SIGFPE;
>         fault_addr = (void __user *) regs->csr_era;
> @@ -432,7 +432,8 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
>         unsigned long era = exception_era(regs);
>         irqentry_state_t state = irqentry_enter(regs);
>
> -       local_irq_enable();
> +       if (regs->csr_prmd & CSR_PRMD_PIE)
> +               local_irq_enable();
>         current->thread.trap_nr = read_csr_excode();
>         if (__get_inst(&opcode, (u32 *)era, user))
>                 goto out_sigsegv;
> @@ -514,7 +515,8 @@ asmlinkage void noinstr do_ri(struct pt_regs *regs)
>         unsigned int __user *era = (unsigned int __user *)exception_era(regs);
>         irqentry_state_t state = irqentry_enter(regs);
>
> -       local_irq_enable();
> +       if (regs->csr_prmd & CSR_PRMD_PIE)
> +               local_irq_enable();
>         current->thread.trap_nr = read_csr_excode();
>
>         if (notify_die(DIE_RI, "RI Fault", regs, 0, current->thread.trap_nr,
> @@ -606,8 +608,8 @@ asmlinkage void noinstr do_fpu(struct pt_regs *regs)
>  {
>         irqentry_state_t state = irqentry_enter(regs);
>
> -       local_irq_enable();
>         die_if_kernel("do_fpu invoked from kernel context!", regs);
> +       local_irq_enable();
>         BUG_ON(is_lsx_enabled());
>         BUG_ON(is_lasx_enabled());
>
> @@ -623,13 +625,13 @@ asmlinkage void noinstr do_lsx(struct pt_regs *regs)
>  {
>         irqentry_state_t state = irqentry_enter(regs);
>
> +       die_if_kernel("do_lsx invoked from kernel context!", regs);
>         local_irq_enable();
>         if (!cpu_has_lsx) {
>                 force_sig(SIGILL);
>                 goto out;
>         }
>
> -       die_if_kernel("do_lsx invoked from kernel context!", regs);
>         BUG_ON(is_lasx_enabled());
>
>         preempt_disable();
> @@ -645,14 +647,13 @@ asmlinkage void noinstr do_lasx(struct pt_regs *regs)
>  {
>         irqentry_state_t state = irqentry_enter(regs);
>
> +       die_if_kernel("do_lasx invoked from kernel context!", regs);
>         local_irq_enable();
>         if (!cpu_has_lasx) {
>                 force_sig(SIGILL);
>                 goto out;
>         }
>
> -       die_if_kernel("do_lasx invoked from kernel context!", regs);
> -
>         preempt_disable();
>         init_restore_lasx();
>         preempt_enable();
> @@ -666,6 +667,7 @@ asmlinkage void noinstr do_lbt(struct pt_regs *regs)
>  {
>         irqentry_state_t state = irqentry_enter(regs);
>
> +       die_if_kernel("do_lbt invoked from kernel context!", regs);
>         local_irq_enable();
>         force_sig(SIGILL);
>         local_irq_disable();
> @@ -677,7 +679,6 @@ asmlinkage void noinstr do_reserved(struct pt_regs *regs)
>  {
>         irqentry_state_t state = irqentry_enter(regs);
>
> -       local_irq_enable();
>         /*
>          * Game over - no way to handle this if it ever occurs. Most probably
>          * caused by a fatal error after another hardware/software error.
> @@ -685,8 +686,8 @@ asmlinkage void noinstr do_reserved(struct pt_regs *regs)
>         pr_err("Caught reserved exception %u on pid:%d [%s] - should not happen\n",
>                 read_csr_excode(), current->pid, current->comm);
>         die_if_kernel("do_reserved exception", regs);
> +       local_irq_enable();
>         force_sig(SIGUNUSED);
> -
>         local_irq_disable();
>
>         irqentry_exit(regs, state);
> --
> 2.34.3
>