Date: Sun, 9 Feb 2014 13:39:07 +0100
From: Ingo Molnar <mingo@kernel.org>
To: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
        hpa@zytor.com, x86@kernel.org
Subject: Re: [PROBLEM] x86: result of verify_local_APIC() is ignored
Message-ID: <20140209123907.GA21208@gmail.com>
References: <20140207004534.GI3232@feynman.vault24.org>
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* Jon <nuxi@vault24.org> wrote:

> In arch/x86/kernel/apic/apic.c there is a function called
> verify_local_APIC() that does some APIC checks. The part where it writes
> to the APIC ID register can cause CPU #15 to not come online under
> VMware ESXi on 32-bit kernels if the virtual hardware version is 8.
> 
> I noticed that Ingo actually removed this exact chunk of code from
> arch/i386/kernel/apic.c in 2.6.4, but since it was left in the x86_64
> copy it came back when the two were merged.
> http://permalink.gmane.org/gmane.linux.kernel.commits.head/27538
> 
> The Intel architecture manuals seem to agree and notes that the recent
> Intel CPUs do not allow writing to the register which means that
> machines are actually failing this check... which doesn't matter becuase
> none of the callers are checking the return value of this function
> anyway.

I guess we could remove that from the 64-bit code too. Would you like 
to send a tested patch?

Thanks,

	Ingo
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