linux-kernel - Re: [PATCH 7/8] KVM: x86: avoid logical

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Message-ID: <20150130142105.GA27414@potion.redhat.com>
Date:	Fri, 30 Jan 2015 15:21:05 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Nadav Amit <namit@...technion.ac.il>,
	Gleb Natapov <gleb@...nel.org>
Subject: Re: [PATCH 7/8] KVM: x86: avoid logical_map when it is invalid

2015-01-30 10:19+0100, Paolo Bonzini:
> On 29/01/2015 22:48, Radim Krčmář wrote:
> > We want to support mixed modes and the easiest solution is to avoid
> > optimizing those weird and unlikely scenarios.
> 
> Hmm, what happens if use maxcpus to disable some CPUs at startup?

Their APICs are kept sw-disabled in xAPIC mode.

>                                                                    Could
> the disabled CPUs remain in xapic mode while the others move to x2apic?

Yes, but it would only matter if the OS set LDR on them.
I mark x2APIC with perfectly configured xAPIC on unused processors as
"weird" ... (Linux 3.18 and 2.6.32 doesn't do it.)
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