From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753274AbcGMPOt (ORCPT ); Wed, 13 Jul 2016 11:14:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56220 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753148AbcGMPOm (ORCPT ); Wed, 13 Jul 2016 11:14:42 -0400 Date: Wed, 13 Jul 2016 17:14:13 +0200 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, "Lan, Tianyu" , Igor Mammedov , Jan Kiszka , Peter Xu , Yang Zhang Subject: Re: [PATCH v3 12/14] KVM: x86: add a flag to disable KVM x2apic broadcast quirk Message-ID: <20160713151413.GD22438@potion> References: <20160712200930.32143-1-rkrcmar@redhat.com> <20160712200930.32143-13-rkrcmar@redhat.com> <4b30aa90-24bb-c5d0-18c0-b1fb4a62014f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4b30aa90-24bb-c5d0-18c0-b1fb4a62014f@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Wed, 13 Jul 2016 15:14:17 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2016-07-13 10:38+0200, Paolo Bonzini: > On 12/07/2016 22:09, Radim Krčmář wrote: >> @@ -619,14 +619,17 @@ static bool kvm_apic_match_logical_addr(struct kvm_lapic *apic, u32 mda) >> /* KVM APIC implementation has two quirks >> * - dest always begins at 0 while xAPIC MDA has offset 24, >> * - IOxAPIC messages have to be delivered (directly) to x2APIC. >> + * >> + * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API. > > --verbose version: > > /* KVM APIC implementation has two quirks > - * - dest always begins at 0 while xAPIC MDA has offset 24, > - * - IOxAPIC messages have to be delivered (directly) to x2APIC. > + * - dest always begins at 0 while xAPIC MDA has offset 24. This is > + * just a quirk in the API and is not problematic. > * > - * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API. > + * - in-kernel IOAPIC messages have to be delivered directly to > + * x2APIC, because the kernel does not support interrupt remapping. > + * In order to support broadcast without interrupt remapping, x2APIC > + * rewrites the destination of non-IPI messages (and also of IPIs sent > + * from xAPIC-mode LAPICs) from APIC_BROADCAST to X2APIC_BROADCAST. KVM doesn't do the operation in parentheses since 394457a928e0 ("KVM: x86: some apic broadcast modes does not work"). Following patches added only !ipi case (I already regret posting them). > + * > + * The broadcast quirk can be disabled with KVM_CAP_X2APIC_API. This is > + * important when userspace wants to use x2APIC-format MSIs, because > + * APIC_BROADCAST (0xff) is a legal route for "cluster 0, CPUs 0-7". > */ > > Sounds good? Except that one bit. (Code alone really can't explain the what happens here.)