linux-kernel - Re: [PATCH 3/3] x86/mce: Use mce_prep_record() helpers for apei_smca_report_x86

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Date: Fri, 14 Jun 2024 17:47:36 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
	tony.luck@...el.com, x86@...nel.org, avadhut.naik@....com,
	john.allen@....com
Subject: Re: [PATCH 3/3] x86/mce: Use mce_prep_record() helpers for
 apei_smca_report_x86_error()

On Mon, Jun 03, 2024 at 06:55:30PM +0200, Borislav Petkov wrote:
> On Mon, Jun 03, 2024 at 10:34:10AM -0400, Yazen Ghannam wrote:

[...]

> > This is to catch the case where there was no break from the loop.
> 
> If the CPU is possible != whether there was a apicid match.
> 
> Here's how you do that and I'd let you figure out why yours doesn't
> always work:
>

I don't see why it won't work. If there is no break, then the iterator
ends by setting the variable past the last valid value.

For example, I ran this on a system with 512 CPUs:

        unsigned int cpu;

	/* Loops over CPUs 0-511. */
        for_each_possible_cpu(cpu)
                pr_info("loop: cpu=%d\n", cpu);

	/* CPU is now set to 512. */
        pr_info("final: cpu=%d\n", cpu);

	/* CPU 512 is not possible. */
        pr_info("CPU %d is %s possible\n", cpu, cpu_possible(cpu) ? "" : "not");

But...I like your suggestion as it is much more explicit. And I might be
missing something. :/

> diff --git a/arch/x86/kernel/cpu/mce/apei.c b/arch/x86/kernel/cpu/mce/apei.c
> index 0cbadfaf2400..3885fe05f01e 100644
> --- a/arch/x86/kernel/cpu/mce/apei.c
> +++ b/arch/x86/kernel/cpu/mce/apei.c
> @@ -66,6 +66,7 @@ EXPORT_SYMBOL_GPL(apei_mce_report_mem_error);
>  int apei_smca_report_x86_error(struct cper_ia_proc_ctx *ctx_info, u64 lapic_id)
>  {
>  	const u64 *i_mce = ((const u64 *) (ctx_info + 1));
> +	bool apicid_found = false;
>  	unsigned int cpu;
>  	struct mce m;
>  
> @@ -98,11 +99,13 @@ int apei_smca_report_x86_error(struct cper_ia_proc_ctx *ctx_info, u64 lapic_id)
>  		return -EINVAL;
>  
>  	for_each_possible_cpu(cpu) {
> -		if (cpu_data(cpu).topo.initial_apicid == lapic_id)
> +		if (cpu_data(cpu).topo.initial_apicid == lapic_id) {
> +			apicid_found = true;
>  			break;
> +		}
>  	}
>  
> -	if (!cpu_possible(cpu))
> +	if (!apicid_found)
>  		return -EINVAL;
>  
>  	mce_prep_record_common(&m);
> 
>

Would you like me to send another revision with this change? Do you have
any other comments?

Thanks,
Yazen