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

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Date:   Thu, 20 Jul 2023 04:18:11 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        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

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;
> >  	}
> >  	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.

Michael