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

[Jinyang He]

On 2022-12-27 15:37, Huacai Chen wrote:
> Hi, Jinyang,
>
> Move die_if_kernel to irq disabled context to solve what?

For more strict logical. If the code flow go to die in die_if_kernel(),
its interrupt state is enable, that means it may cause schedule.
So I think it is better to call die_if_kernel() firstly.


>   And LBT is
> surely allowed to be triggered in kernel context.

I'm not familar with lbt, I just not see any lbt codes in kernel. Plz,
how lbt exception triggered, and how kernel trigger lbt exception?


Thanks,

Jinyang


> Huacai
>
> On Wed, Dec 21, 2022 at 3:43 PM Jinyang He <hejinyang@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> > ---
> >   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