Re: [PATCH v4] powerpc/traps: Enhance readability for trap types

[Nicholas Piggin]

Thanks for working on this, I think it's a nice cleanup and helps
non-powerpc people understand the code a bit better.

Excerpts from Xiongwei Song's message of April 10, 2021 12:28 am:
> From: Xiongwei Song <sxwjean@xxxxxxxxx>
> 
> Create a new header named traps.h, define macros to list ppc interrupt
> types in traps.h, replace the references of the trap hex values with these
> macros.
> 
> Referred the hex numbers in arch/powerpc/kernel/exceptions-64e.S,
> arch/powerpc/kernel/exceptions-64s.S and
> arch/powerpc/include/asm/kvm_asm.h.
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>

It now looks like lkp asked for this whole cleanup patch. I would
put [kernel test robot <lkp@xxxxxxxxx>] in your v3->4 changelog
item.

> Signed-off-by: Xiongwei Song <sxwjean@xxxxxxxxx>
> ---
> 
> v3-v4:
> Fix compile issue:
> arch/powerpc/kernel/process.c:1473:14: error: 'INTERRUPT_MACHINE_CHECK' undeclared (first use in this function); did you mean 'TAINT_MACHINE_CHECK'?
> I didn't add "Reported-by: kernel test robot <lkp@xxxxxxxxx>" here,
> because it's improper for this patch.

[...]

> diff --git a/arch/powerpc/include/asm/traps.h b/arch/powerpc/include/asm/traps.h
> new file mode 100644
> index 000000000000..2e64e10afcef
> --- /dev/null
> +++ b/arch/powerpc/include/asm/traps.h
> @@ -0,0 +1,32 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_PPC_TRAPS_H
> +#define _ASM_PPC_TRAPS_H

These could go in interrupt.h.

> +#if defined(CONFIG_BOOKE) || defined(CONFIG_4xx)
> +#define INTERRUPT_MACHINE_CHECK   0x000
> +#define INTERRUPT_CRITICAL_INPUT  0x100
> +#define INTERRUPT_ALTIVEC_UNAVAIL 0x200
> +#define INTERRUPT_PERFMON         0x260
> +#define INTERRUPT_DOORBELL        0x280
> +#define INTERRUPT_DEBUG           0xd00
> +#else
> +#define INTERRUPT_SYSTEM_RESET    0x100
> +#define INTERRUPT_MACHINE_CHECK   0x200

[...]

> @@ -1469,7 +1470,9 @@ static void __show_regs(struct pt_regs *regs)
>  	trap = TRAP(regs);
>  	if (!trap_is_syscall(regs) && cpu_has_feature(CPU_FTR_CFAR))
>  		pr_cont("CFAR: "REG" ", regs->orig_gpr3);
> -	if (trap == 0x200 || trap == 0x300 || trap == 0x600) {
> +	if (trap == INTERRUPT_MACHINE_CHECK ||
> +	    trap == INTERRUPT_DATA_STORAGE ||
> +	    trap == INTERRUPT_ALIGNMENT) {
>  		if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
>  			pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, regs->dsisr);
>  		else

This is now a change in behaviour because previously BOOKE/4xx tested
0x200, but now it tests 0.

That looks wrong for 4xx. 64e does put 0x000 there but I wonder if it 
should use 0x200 instead. Bit difficult to test this stuff, I do have
some MCE injection patches for QEMU for 64s, might be able to look at
porting them to 64e although I have no idea about booke machine checks.

Anyway I don't think this patch should change generated code at all.
Either change the code first with smaller patches, or make sure you
keep the tests the same.

Thanks,
Nick