From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760580AbZCPSbW (ORCPT ); Mon, 16 Mar 2009 14:31:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754316AbZCPSbK (ORCPT ); Mon, 16 Mar 2009 14:31:10 -0400 Received: from mx2.redhat.com ([66.187.237.31]:47722 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754529AbZCPSbI (ORCPT ); Mon, 16 Mar 2009 14:31:08 -0400 Date: Mon, 16 Mar 2009 15:30:00 -0300 From: Marcelo Tosatti To: Avi Kivity Cc: Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] kvm/x86: check KVM_REQ_TLB_FLUSH with irqs disabled Message-ID: <20090316183000.GC3783@amt.cnet> References: <1237208625-2657-1-git-send-email-joerg.roedel@amd.com> <49BE5054.6040707@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49BE5054.6040707@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 16, 2009 at 03:12:52PM +0200, Avi Kivity wrote: > Joerg Roedel wrote: >> For KVM remote TLB flushes we need to check the KVM_REQ_TLB_FLUSH >> request flag when the irqs are already disabled. Otherwise there is a >> small window of time for a race condition where we may enter a guest >> without doing a requested TLB flush. >> >> @@ -3108,8 +3108,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) >> kvm_write_guest_time(vcpu); >> if (test_and_clear_bit(KVM_REQ_MMU_SYNC, &vcpu->requests)) >> kvm_mmu_sync_roots(vcpu); >> - if (test_and_clear_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests)) >> - kvm_x86_ops->tlb_flush(vcpu); >> if (test_and_clear_bit(KVM_REQ_REPORT_TPR_ACCESS, >> &vcpu->requests)) { >> kvm_run->exit_reason = KVM_EXIT_TPR_ACCESS; >> @@ -3133,6 +3131,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) >> local_irq_disable(); >> + if (test_and_clear_bit(KVM_REQ_TLB_FLUSH, &vcpu->requests)) >> + kvm_x86_ops->tlb_flush(vcpu); >> + >> if (vcpu->requests || need_resched() || signal_pending(current)) { >> local_irq_enable(); >> preempt_enable(); >> > > If we lost the race and someone sets a bit after the test, then the test > immediately above will pick this up retry the bit tests. BTW, I've wondered if the local_irq_enable in svm_vcpu_run is safe: clgi(); local_irq_enable(); There is no way that an interrupt can be handled there without an exit, right?