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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     "x86@kernel.org" <x86@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Wei Liu <wei.liu@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Juergen Gross <jgross@suse.com>
Subject: RE: [patch 19/58] x86/apic: Get rid of apic_phys
In-Reply-To: <BYAPR21MB1688E1BDE9B6D1225E590FF1D73EA@BYAPR21MB1688.namprd21.prod.outlook.com>
References: <20230717223049.327865981@linutronix.de>
 <20230717223224.207131427@linutronix.de> <87edl5xt2n.ffs@tglx>
 <BYAPR21MB1688E1BDE9B6D1225E590FF1D73EA@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Thu, 20 Jul 2023 10:03:20 +0200
Message-ID: <874jlz3t87.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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

> From: Thomas Gleixner <tglx@linutronix.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