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Message-ID: <b4f0e874-1e35-e523-8e5a-710bc54af52d@suse.com>
Date: Mon, 31 Jul 2023 15:10:21 +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 50/58] x86/apic: Provide common init infrastructure
On 31.07.23 15:01, Thomas Gleixner wrote:
> On Mon, Jul 31 2023 at 13:31, Juergen Gross wrote:
>> On 24.07.23 15:35, Thomas Gleixner wrote:
>>> static void __init xen_apic_check(void)
>>> {
>>> - if (apic == &xen_pv_apic)
>>> - return;
>>> -
>>> - pr_info("Switched APIC routing from %s to %s.\n", apic->name,
>>> - xen_pv_apic.name);
>>> - apic = &xen_pv_apic;
>>> + apic_install_driver(&xen_pv_apic);
>>> }
>>> +
>>> void __init xen_init_apic(void)
>>> {
>>> x86_apic_ops.io_apic_read = xen_io_apic_read;
>>> /* On PV guests the APIC CPUID bit is disabled so none of the
>>> * routines end up executing. */
>>> if (!xen_initial_domain())
>>> - apic = &xen_pv_apic;
>>> + apic_install_driver(&xen_pv_apic);
>>
>> This is working, but it produces a WARN() splat when booting as an unprivileged
>> Xen PV guest from static_call patching (static_call_init() hasn't been called
>> yet).
>
> Duh, yes. It's too early.
>
>> The diff below on top is fixing the issue:
>>
>> diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c
>> index 1838aefc632f..84f24268670b 100644
>> --- a/arch/x86/xen/apic.c
>> +++ b/arch/x86/xen/apic.c
>> @@ -163,14 +163,18 @@ static void __init xen_apic_check(void)
>> apic_install_driver(&xen_pv_apic);
>> }
>>
>> +void __init xen_apic_install(void)
>> +{
>> + /*
>> + * On PV guests the APIC CPUID bit is disabled so none of the
>> + * routines end up executing.
>> + */
>> + apic_install_driver(&xen_pv_apic);
>> +}
>> +
>> void __init xen_init_apic(void)
>> {
>> x86_apic_ops.io_apic_read = xen_io_apic_read;
>> - /* On PV guests the APIC CPUID bit is disabled so none of the
>> - * routines end up executing. */
>> - if (!xen_initial_domain())
>> - apic_install_driver(&xen_pv_apic);
>> -
>> x86_platform.apic_post_init = xen_apic_check;
>> }
>> apic_driver(xen_pv_apic);
>
> I wonder whether this explicit install is actually needed at all.
> Shouldn't the driver be installed via the APIC probing mechanism
> automagically?
Only in case x86_init.irq.intr_mode_init is set appropriately. Today it is
a nop for Xen PV, but that can be changed. I'll have a look.
Juergen
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