linux-kernel - Re: [patch V2 16/58] x86/apic: Sanitize num

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Date:   Mon, 31 Jul 2023 20:19:25 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Andrew Cooper <andrew.cooper3@...rix.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wei Liu <wei.liu@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Peter Keresztes Schmidt <peter@...esztesschmidt.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V2 16/58] x86/apic: Sanitize num_processors handling

On 31.07.23 17:57, Thomas Gleixner wrote:
> On Mon, Jul 31 2023 at 14:50, Thomas Gleixner wrote:
>> Why can't XENPV pretend that it has a smp configuration detected,
>> i.e. setting smp_found_config as any other special get_smp_config()
>> implementation does?
> 
> The below should do the trick, no?

Something like that, yes.

I'm just hunting another regression in the series. With patch 23 of the
topology series applied the APs of a Xen PV guests won't be onlined. I
guess this is due to missing topology data initialization somewhere in
the Xen related code.

I'll check your suggestion after finding the reason for the regression.


Juergen

> 
> 
> --- a/arch/x86/xen/smp_pv.c
> +++ b/arch/x86/xen/smp_pv.c
> @@ -182,7 +182,8 @@ static void __init _get_smp_config(unsig
>   	if (subtract)
>   		set_nr_cpu_ids(nr_cpu_ids - subtract);
>   #endif
> -
> +	/* Pretend to be a proper enumerated system */
> +	smp_found_config = 1;
>   }
>   
>   static void __init xen_pv_smp_prepare_boot_cpu(void)


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