From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joerg Roedel <joerg.roedel@amd.com>
Subject: Re: [PATCH] kvm/x86: check KVM_REQ_TLB_FLUSH with irqs disabled
Date: Mon, 16 Mar 2009 15:11:34 +0100
Message-ID: <20090316141134.GI6159@amd.com>
References: <1237208625-2657-1-git-send-email-joerg.roedel@amd.com> <49BE5054.6040707@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: QUOTED-PRINTABLE
Cc: Marcelo Tosatti <mtosatti@redhat.com>, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
To: Avi Kivity <avi@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from tx2ehsobe003.messaging.microsoft.com ([65.55.88.13]:26565 "EHLO
	TX2EHSOBE006.bigfish.com" rhost-flags-OK-OK-OK-FAIL)
	by vger.kernel.org with ESMTP id S1753908AbZCPOMu convert rfc822-to-8bit
	(ORCPT <rfc822;kvm@vger.kernel.org>);
	Mon, 16 Mar 2009 10:12:50 -0400
Content-Disposition: inline
In-Reply-To: <49BE5054.6040707@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.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 *v=
cpu, 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 =3D KVM_EXIT_TPR_ACCESS;
> >@@ -3133,6 +3131,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *v=
cpu, 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();
> > =20
>=20
> 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.
>

Ah true. Sorry for the noise.

--=20
           | Advanced Micro Devices GmbH
 Operating | Karl-Hammerschmidt-Str. 34, 85609 Dornach bei M=C3=BCnchen
 System    |=20
 Research  | Gesch=C3=A4ftsf=C3=BChrer: Jochen Polster, Thomas M. McCoy=
, Giuliano Meroni
 Center    | Sitz: Dornach, Gemeinde Aschheim, Landkreis M=C3=BCnchen
           | Registergericht M=C3=BCnchen, HRB Nr. 43632