From: ebiederm@xmission.com (Eric W. Biederman)
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>,
linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
x86@kernel.org, mingo@elte.hu, tglx@linutronix.de,
len.brown@intel.com, fenghua.yu@intel.com, vgoyal@redhat.com,
grant.likely@secretlab.ca, rob.herring@calxeda.com
Subject: Re: [PATCH v1 2/2] x86, apic: Disable BSP if boot cpu is AP
Date: Mon, 22 Oct 2012 14:29:25 -0700 [thread overview]
Message-ID: <87mwze8abu.fsf@xmission.com> (raw)
In-Reply-To: <5085B0D0.9020508@zytor.com> (H. Peter Anvin's message of "Mon, 22 Oct 2012 13:47:12 -0700")
"H. Peter Anvin" <hpa@zytor.com> writes:
> On 10/22/2012 01:43 PM, Eric W. Biederman wrote:
>>
>> The reason the BIOSen go wonky is the INIT cause the cpu to go to the
>> reset vector at 4G-16 bytes. So it is very much expected that the
>> BIOSen start acting like you just came out of reset.
>>
>> If you can clear bit 8 of IA32_APIC_BASE_MSR and inform the cpu to not
>> send the cpu to 4G-16 bytes and instead send the cpu into it's magic
>> startup-ipi-wait mode then the BIOSen will not be involved on that path.
>>
>> It is a simple question of does the cpu support clearing bit 8
>> meaningfully.
>>
>> If the cpu allows bit 8 to be cleared and sends the cpu to the reset
>> vector on receipt of the INIT IPI I would call that a deviation from the
>> x86 cpu specification.
>>
>> So clearing bit 8 is not a question about BIOSen it is a question of can
>> we avoid the BIOSen, by using an obscure under-documented cpu feature.
>>
>
> As I said, I thought Fenghua tried that but it didn't work, experimentally.
Fair enough. You described the problem with clearing bit 8 in a weird
way.
If the best we can muster are fuzzy memories it may be worth revisiting.
Perhaps it works on enough cpu models to be interesting.
Eric
next prev parent reply other threads:[~2012-10-22 21:29 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-16 4:35 [PATCH v1 0/2] x86, apic: Disable BSP if boot cpu is AP HATAYAMA Daisuke
2012-10-16 4:35 ` [PATCH v1 1/2] x86, apic: Introduce boot_cpu_is_bsp indicating whether boot cpu is BSP or not HATAYAMA Daisuke
2012-10-16 4:35 ` [PATCH v1 2/2] x86, apic: Disable BSP if boot cpu is AP HATAYAMA Daisuke
2012-10-22 20:04 ` Eric W. Biederman
2012-10-22 20:16 ` H. Peter Anvin
2012-10-22 20:31 ` Eric W. Biederman
2012-10-22 20:33 ` H. Peter Anvin
2012-10-22 20:38 ` H. Peter Anvin
2012-10-22 20:43 ` Eric W. Biederman
2012-10-22 20:47 ` H. Peter Anvin
2012-10-22 21:29 ` Eric W. Biederman [this message]
2012-10-23 0:35 ` H. Peter Anvin
2012-10-26 3:24 ` HATAYAMA Daisuke
2012-10-26 4:13 ` Eric W. Biederman
2013-03-11 1:07 ` HATAYAMA Daisuke
2013-03-11 2:13 ` HATAYAMA Daisuke
2013-03-11 4:11 ` H. Peter Anvin
2012-10-16 4:51 ` [PATCH v1 0/2] " Yu, Fenghua
2012-10-16 5:03 ` HATAYAMA Daisuke
2012-10-16 5:14 ` Yu, Fenghua
2012-10-16 6:38 ` HATAYAMA Daisuke
2012-10-22 16:02 ` H. Peter Anvin
2012-10-16 5:15 ` HATAYAMA Daisuke
2012-10-17 14:12 ` Vivek Goyal
2012-10-18 3:08 ` HATAYAMA Daisuke
2012-10-18 14:14 ` Vivek Goyal
2012-10-19 3:20 ` HATAYAMA Daisuke
2012-10-19 15:17 ` Vivek Goyal
2012-10-22 6:32 ` HATAYAMA Daisuke
2012-10-22 18:37 ` Vivek Goyal
2012-10-22 17:10 ` Michael Holzheu
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