From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH v5] enable x2APIC without interrupt remapping under KVM Date: Fri, 3 Jul 2009 10:29:05 +0200 Message-ID: <20090703082905.GF21833@elte.hu> References: <20090701133007.GC27539@redhat.com> <1246482017.27006.10670.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Gleb Natapov , "linux-kernel@vger.kernel.org" , Sheng Yang , "kvm@vger.kernel.org" , "avi@redhat.com" To: Suresh Siddha Return-path: Received: from mx3.mail.elte.hu ([157.181.1.138]:54542 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755858AbZGCI3N (ORCPT ); Fri, 3 Jul 2009 04:29:13 -0400 Content-Disposition: inline In-Reply-To: <1246482017.27006.10670.camel@localhost.localdomain> Sender: kvm-owner@vger.kernel.org List-ID: * Suresh Siddha wrote: > On Wed, 2009-07-01 at 06:30 -0700, Gleb Natapov wrote: > > KVM would like to provide x2APIC interface to a guest without emulating > > interrupt remapping device. The reason KVM prefers guest to use x2APIC > > is that x2APIC interface is better virtualizable and provides better > > performance than mmio xAPIC interface: > > > > - msr exits are faster than mmio (no page table walk, emulation) > > - no need to read back ICR to look at the busy bit > > - one 64 bit ICR write instead of two 32 bit writes > > - shared code with the Hyper-V paravirt interface > > > > Included patch changes x2APIC enabling logic to enable it even if IR > > initialization failed, but kernel runs under KVM and no apic id is > > greater than 255 (if there is one spec requires BIOS to move to x2apic > > mode before starting an OS). > > > > Signed-off-by: Gleb Natapov > > Acked-by: Suresh Siddha Now, since this affects core x86 APIC code non-trivially so should submitted to and go via the x86 tree. (Can prepare a special branch with just this change if KVM tree wants/needs to pull it before v2.6.32.) Ingo