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

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Date:   Mon, 31 Jul 2023 14:50:07 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Juergen Gross <jgross@...e.com>,
        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 Mon, Jul 31 2023 at 12:17, Juergen Gross wrote:
> On 24.07.23 15:34, Thomas Gleixner wrote:
> This is introducing a regression for Xen PV guests: those have no ACPI
> tables, so smp_found_config will be 0. OTOH num_processors has been set
> already using hypervisor data, so setting num_processors to 1 here will
> overwrite the previous setting.
>
> Below diff on top is fixing the problem:

Fixing? You can't be serious about that.

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?

XENPV is already a major pain to deal with. No need to expand the
related insanity all over the place.

Thanks,

        tglx