Re: [PATCH v1 2/2] x86, apic: Disable BSP if boot cpu is AP

From: H. Peter Anvin
Date: Mon Oct 22 2012 - 16:47:42 EST

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.


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