Re: [PATCH V5 07/11] riscv: convert to generic entry

Peter Zijlstra
2022-09-19T13:34:52Z

On Sun, Sep 18, 2022 at 11:52:42AM -0400, guoren@kernel.org wrote:

> @@ -123,18 +126,22 @@ int handle_misaligned_store(struct pt_regs *regs);
>
> asmlinkage void __trap_section do_trap_load_misaligned(struct pt_regs *regs)
> {
> + irqentry_state_t state = irqentry_enter(regs);
> if (!handle_misaligned_load(regs))
> return;
> do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
> "Oops - load address misaligned");
> + irqentry_exit(regs, state);
> }
>
> asmlinkage void __trap_section do_trap_store_misaligned(struct pt_regs *regs)
> {
> + irqentry_state_t state = irqentry_enter(regs);
> if (!handle_misaligned_store(regs))
> return;
> do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
> "Oops - store (or AMO) address misaligned");
> + irqentry_exit(regs, state);
> }
> #endif
> DO_ERROR_INFO(do_trap_store_fault,
> @@ -158,6 +165,8 @@ static inline unsigned long get_break_insn_length(unsigned long pc)
>
> asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
> {
> + irqentry_state_t state = irqentry_enter(regs);
> +
> #ifdef CONFIG_KPROBES
> if (kprobe_single_step_handler(regs))
> return;

FWIW; on x86 I've classified many of the 'from-kernel' traps as
NMI-like, since those traps can happen from any context, including with
IRQs disabled.

The basic shape of the trap handlers looks a little like:

if (user_mode(regs)) {
irqenrty_enter_from_user_mode(regs);
do_user_trap();
irqentry_exit_to_user_mode(regs);
} else {
irqentry_state_t state = irqentry_nmi_enter(regs);
do_kernel_trap();
irqentry_nmi_exit(regs, state);
}

Not saying you have to match Risc-V in this patch-set, just something to
consider.