From: Cao jin <caoj.fnst@cn.fujitsu.com>
To: Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
Subject: Re: Is this code chunk in init_apic_mappings() superfluous?
Date: Wed, 11 Mar 2020 20:39:37 +0800 [thread overview]
Message-ID: <3859d094-676d-7e17-0655-9d0091a0d47c@cn.fujitsu.com> (raw)
In-Reply-To: <87imjg9zgp.fsf@nanos.tec.linutronix.de>
On 3/7/20 7:27 PM, Thomas Gleixner wrote:
> Cao jin <caoj.fnst@cn.fujitsu.com> writes:
>> Hi,
>>
>> I am trying to figure the following code chunk out:
>>
>> if (x2apic_mode) {
>> boot_cpu_physical_apicid = read_apic_id();
>> return;
>> }
>>
>> As my understanding, even in x2APIC mode, boot_cpu_physical_apicid is
>> also got via early_acpi_process_madt --> ... --> register_lapic_address,
>> so, is it for any corner case I am not aware?
>
> The case when there are neither ACPI nor valid mptables. Unlikely, but
> possible in theory.
>
I noticed this case in its calling comments, but failed to associate it
with a x2APIC...
So init_apic_mapping() is for 2 corner cases that doesn't map APIC
register before: one you mentioned here, and MP default configuration
the other.
Thanks Thomas.
--
Sincerely,
Cao jin
prev parent reply other threads:[~2020-03-11 12:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-05 12:44 Is this code chunk in init_apic_mappings() superfluous? Cao jin
2020-03-07 11:27 ` Thomas Gleixner
2020-03-11 12:39 ` Cao jin [this message]
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