From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759576AbdACQO4 (ORCPT ); Tue, 3 Jan 2017 11:14:56 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51750 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759542AbdACQOw (ORCPT ); Tue, 3 Jan 2017 11:14:52 -0500 Subject: Re: [PATCH v2 3/6] KVM: x86: make pic setup code look like ioapic setup To: David Hildenbrand , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <20161216151006.11776-1-rkrcmar@redhat.com> <20161216151006.11776-4-rkrcmar@redhat.com> <2cca2bc6-2702-0b2f-e744-f86cbdd80ef5@redhat.com> From: Paolo Bonzini Message-ID: Date: Tue, 3 Jan 2017 17:12:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <2cca2bc6-2702-0b2f-e744-f86cbdd80ef5@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 03 Jan 2017 16:12:35 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/01/2017 14:04, David Hildenbrand wrote: > Am 16.12.2016 um 16:10 schrieb Radim Krčmář: >> We don't treat kvm->arch.vpic specially anymore, so the setup can look >> like ioapic. This gets a bit more information out of return values. > > This originally saved us from a race condition as far as I can > reconstruct from the commit history. Think the problem was > vpic being set but routes not being set up yet. > > commit 71ba994c94a81c37185ef2fb5190844286ba9aca > Author: Paolo Bonzini > Date: Wed Jul 29 12:31:15 2015 +0200 > > KVM: x86: clean/fix memory barriers in irqchip_in_kernel > > The memory barriers are trying to protect against concurrent RCU-based > interrupt injection, but the IRQ routing table is not valid at the time > kvm->arch.vpic is written. Fix this by writing kvm->arch.vpic last. > kvm_destroy_pic then need not set kvm->arch.vpic to NULL; modify it > to take a struct kvm_pic* and reuse it if the IOAPIC creation fails. > > Signed-off-by: Paolo Bonzini > > I assume that this is now fixed via the irqchip_mode, as it is stored > last? If so, I really like this patch :) Yes, the previous patch referred to that when it said "irqchip_in_kernel() tried to save a bit by reusing pic_irqchip()", and what this commit message means by "not trteating kvm->arch.vpic specially anymore". Paolo