From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v2 3/6] KVM: x86: make pic setup code look like ioapic setup Date: Tue, 3 Jan 2017 17:12:33 +0100 Message-ID: References: <20161216151006.11776-1-rkrcmar@redhat.com> <20161216151006.11776-4-rkrcmar@redhat.com> <2cca2bc6-2702-0b2f-e744-f86cbdd80ef5@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit To: David Hildenbrand , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <2cca2bc6-2702-0b2f-e744-f86cbdd80ef5@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.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