linux-kernel - RE: [patch 19/58] x86/apic: Get rid of apic

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Message-ID: <874jlz3t87.ffs@tglx>
Date:   Thu, 20 Jul 2023 10:03:20 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.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>,
        Juergen Gross <jgross@...e.com>
Subject: RE: [patch 19/58] x86/apic: Get rid of apic_phys

On Thu, Jul 20 2023 at 04:18, Michael Kelley wrote:

> From: Thomas Gleixner <tglx@...utronix.de> Sent: Tuesday, July 18, 2023 6:12 AM
>> 
>> On Tue, Jul 18 2023 at 01:15, Thomas Gleixner wrote:
>> > @@ -1921,7 +1922,6 @@ static __init void try_to_enable_x2apic(
>> >  		 * be addressed must not be brought online.
>> >  		 */
>> >  		x2apic_set_max_apicid(apic_limit);
>> > -		x2apic_phys = 1;

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This hunk _IS_ wrong and needs to be
reverted obvioulsy.

>> >  	}
>> >  	x2apic_enable();
>> >  }
>> 
>> This hunk is obviously bogus. I just noticed on a VM which takes this
>> code path...
>
> I'm testing guests on Hyper-V.  The case where the x2apic is enabled
> in the BIOS works, but when the x2apic must be enabled by Linux,
> the VMbus drivers never get initialized and things go downhill from
> there. Your comment above is somewhat cryptic (as I haven't studied
> the patches in detail), but I'm guessing it explains the failure I'm seeing.
>
> Let me know if I should debug the failure I'm seeing.  Otherwise
> I'll wait for a new version and try again.

Can you add that line back and retest?

Thanks,

        tglx