Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753219AbZFOCG7 (ORCPT ); Sun, 14 Jun 2009 22:06:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750935AbZFOCGw (ORCPT ); Sun, 14 Jun 2009 22:06:52 -0400 Received: from claw.goop.org ([74.207.240.146]:46150 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750838AbZFOCGv (ORCPT ); Sun, 14 Jun 2009 22:06:51 -0400 Message-ID: <4A35ACB3.9040501@goop.org> Date: Sun, 14 Jun 2009 19:06:43 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2 MIME-Version: 1.0 To: "Eric W. Biederman" CC: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , the arch/x86 maintainers , Linux Kernel Mailing List , Xen-devel Subject: Re: [PATCH RFC] x86/acpi: don't ignore I/O APICs just because there's no local APIC References: <4A329CF8.4050502@goop.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1782 Lines: 41 On 06/12/09 13:35, Eric W. Biederman wrote: > Jeremy Fitzhardinge writes: > > >> Parse the ACPI MADT for I/O APIC information, even if the cpu has no >> (apparent) local APIC (ie, the CPU's APIC feature flag is clear). >> >> In principle, the local APIC and the I/O APIC are distinct (but related) >> components, which can be independently present. >> >> In practice this can happen in a Xen system, where the hypervisor has >> full control over the local APICs, and delivers interrupts initiated by >> the I/O APICs via Xen's event channel mechanism. >> > > Xen is giving us a semi bogus acpi table? > No, not really. The guest is reading the real BIOS-provided ACPI tables, but Xen is clobbering the APIC feature in CPUID so the virtual CPU doesn't appear to have a usable local APIC. Xen itself doesn't care very much about interrupt routing or ACPI, and doesn't make any attempt to read or parse the ACPI data itself (except for very basic things like the APIC addresses). > What is the paravirt configuration model with Xen? Is it documented > somewhere? > Not very well. The basic idea is that Xen owns the local apics, and does things like vector allocation. The guest kernel is responsible for asking for a vector, and doing the appropriate IO APIC programming, and binding that vector to an event channel. The interrupt is then delivered via the normal event channel mechanism already in place to deal with all the other event types an unprivileged domain can get. J -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/