From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: x86: always exit on EOIs for interrupts listed in the IOAPIC redir table Date: Wed, 06 Aug 2014 16:08:38 +0200 Message-ID: <53E236E6.6050206@redhat.com> References: <1406736728-8516-1-git-send-email-pbonzini@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "alex.williamson@redhat.com" , "kvm@vger.kernel.org" , "stable@vger.kernel.org" To: "Zhang, Yang Z" , "linux-kernel@vger.kernel.org" Return-path: In-Reply-To: Sender: stable-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Il 06/08/2014 16:03, Zhang, Yang Z ha scritto: > Paolo Bonzini wrote on 2014-07-31: >> Probably, the guest is masking the interrupt in the redirection table in >> the interrupt routine, i.e. while the interrupt is set in a LAPIC's ISR. >> The simplest fix is to ignore the masking state, we would rather have >> an unnecessary exit rather than a missed IRQ ACK and anyway IOAPIC >> interrupts are not as performance-sensitive as for example MSIs. > > I feel this fixing may hurt performance in some cases. If the mask > bit is set, this means the vector in this entry may be used by other > devices(like a assigned device). But here you set it in eoi exit bitmap > and this will cause vmexit on each EOI which should not happen. Note that this *was* reported on an assigned device. IOAPIC should not be a performance-sensitive path. High-performance assigned devices should be using MSIs. Paolo