linux-kernel - Re: [PATCH 1/5] riscv: misaligned: factorize trap handling

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Message-ID: <ba11b910-9959-4845-b3a3-dd9a52466823@ghiti.fr>
Date: Mon, 21 Apr 2025 09:06:59 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Clément Léger <cleger@...osinc.com>,
 "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:RISC-V ARCHITECTURE" <linux-riscv@...ts.infradead.org>,
 "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Cc: Jonathan Corbet <corbet@....net>, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
 Albert Ou <aou@...s.berkeley.edu>, Shuah Khan <shuah@...nel.org>,
 Andrew Jones <ajones@...tanamicro.com>,
 Samuel Holland <samuel.holland@...ive.com>,
 Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/5] riscv: misaligned: factorize trap handling

Hi Clément,


On 14/04/2025 14:34, Clément Léger wrote:
> misaligned accesses traps are not nmi and should be treated as normal
> one using irqentry_enter()/exit().


All the traps that come from kernel mode are treated as nmi as it was 
suggested by Peter here: 
https://lore.kernel.org/linux-riscv/Yyhv4UUXuSfvMOw+@hirez.programming.kicks-ass.net/

I don't know the differences between irq_nmi_entry/exit() and 
irq_entry/exit(), so is that still correct to now treat the kernel traps 
as non-nmi?

Thanks,

Alex


> Since both load/store and user/kernel
> should use almost the same path and that we are going to add some code
> around that, factorize it.
>
> Signed-off-by: Clément Léger<cleger@...osinc.com>
> ---
>   arch/riscv/kernel/traps.c | 49 ++++++++++++++++-----------------------
>   1 file changed, 20 insertions(+), 29 deletions(-)
>
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index 8ff8e8b36524..55d9f3450398 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -198,47 +198,38 @@ asmlinkage __visible __trap_section void do_trap_insn_illegal(struct pt_regs *re
>   DO_ERROR_INFO(do_trap_load_fault,
>   	SIGSEGV, SEGV_ACCERR, "load access fault");
>   
> -asmlinkage __visible __trap_section void do_trap_load_misaligned(struct pt_regs *regs)
> +enum misaligned_access_type {
> +	MISALIGNED_STORE,
> +	MISALIGNED_LOAD,
> +};
> +
> +static void do_trap_misaligned(struct pt_regs *regs, enum misaligned_access_type type)
>   {
> -	if (user_mode(regs)) {
> -		irqentry_enter_from_user_mode(regs);
> +	irqentry_state_t state = irqentry_enter(regs);
>   
> +	if (type ==  MISALIGNED_LOAD) {
>   		if (handle_misaligned_load(regs))
>   			do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
> -			      "Oops - load address misaligned");
> -
> -		irqentry_exit_to_user_mode(regs);
> +				      "Oops - load address misaligned");
>   	} else {
> -		irqentry_state_t state = irqentry_nmi_enter(regs);
> -
> -		if (handle_misaligned_load(regs))
> +		if (handle_misaligned_store(regs))
>   			do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
> -			      "Oops - load address misaligned");
> -
> -		irqentry_nmi_exit(regs, state);
> +				      "Oops - store (or AMO) address misaligned");
>   	}
> +
> +	irqentry_exit(regs, state);
>   }
>   
> -asmlinkage __visible __trap_section void do_trap_store_misaligned(struct pt_regs *regs)
> +asmlinkage __visible __trap_section void do_trap_load_misaligned(struct pt_regs *regs)
>   {
> -	if (user_mode(regs)) {
> -		irqentry_enter_from_user_mode(regs);
> -
> -		if (handle_misaligned_store(regs))
> -			do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
> -				"Oops - store (or AMO) address misaligned");
> -
> -		irqentry_exit_to_user_mode(regs);
> -	} else {
> -		irqentry_state_t state = irqentry_nmi_enter(regs);
> -
> -		if (handle_misaligned_store(regs))
> -			do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
> -				"Oops - store (or AMO) address misaligned");
> +	do_trap_misaligned(regs, MISALIGNED_LOAD);
> +}
>   
> -		irqentry_nmi_exit(regs, state);
> -	}
> +asmlinkage __visible __trap_section void do_trap_store_misaligned(struct pt_regs *regs)
> +{
> +	do_trap_misaligned(regs, MISALIGNED_STORE);
>   }
> +
>   DO_ERROR_INFO(do_trap_store_fault,
>   	SIGSEGV, SEGV_ACCERR, "store (or AMO) access fault");
>   DO_ERROR_INFO(do_trap_ecall_s,