Return-Path: <linux-kernel-owner+w=401wt.eu-S933280AbZLOSXT@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S933280AbZLOSXT (ORCPT <rfc822;w@1wt.eu>);
	Tue, 15 Dec 2009 13:23:19 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760778AbZLOSXS
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Tue, 15 Dec 2009 13:23:18 -0500
Received: from mx1.redhat.com ([209.132.183.28]:46461 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1760796AbZLOSXQ (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Tue, 15 Dec 2009 13:23:16 -0500
Date: Tue, 15 Dec 2009 16:21:39 -0200
From: Marcelo Tosatti <mtosatti@redhat.com>
To: Zachary Amsden <zamsden@redhat.com>
Cc: kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>,
       Joerg Roedel <joerg.roedel@amd.com>, linux-kernel@vger.kernel.org,
       Dor Laor <dlaor@redhat.com>
Subject: Re: [PATCH RFC: kvm tsc virtualization 15/20] Fix longstanding
	races
Message-ID: <20091215182139.GA14005@amt.cnet>
References: <1260850127-9766-7-git-send-email-zamsden@redhat.com> <1260850127-9766-8-git-send-email-zamsden@redhat.com> <1260850127-9766-9-git-send-email-zamsden@redhat.com> <1260850127-9766-10-git-send-email-zamsden@redhat.com> <1260850127-9766-11-git-send-email-zamsden@redhat.com> <1260850127-9766-12-git-send-email-zamsden@redhat.com> <1260850127-9766-13-git-send-email-zamsden@redhat.com> <1260850127-9766-14-git-send-email-zamsden@redhat.com> <1260850127-9766-15-git-send-email-zamsden@redhat.com> <1260850127-9766-16-git-send-email-zamsden@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1260850127-9766-16-git-send-email-zamsden@redhat.com>
User-Agent: Mutt/1.5.19 (2009-01-05)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2090
Lines: 47

On Mon, Dec 14, 2009 at 06:08:42PM -1000, Zachary Amsden wrote:

<snip>

+               atomic_set(&per_cpu(cpu_tsc_synchronized, freq->cpu),
0);
+               spin_lock(&kvm_lock);
+               list_for_each_entry(kvm, &vm_list, vm_list) {
+                       kvm_for_each_vcpu(i, vcpu, kvm) {
+                               if (vcpu->cpu != freq->cpu)
+                                       continue;
+                               if (vcpu->cpu != smp_processor_id())
+                                       send_ipi++;
+                               kvm_request_guest_time_update(vcpu);

There is some overlap here between KVM_REQ_KVMCLOCK_UPDATE and
cpu_tsc_synchronized. Its the same information (frequency for a CPU has
changed) stored in two places.

Later you do:

                spin_lock(&kvm_lock);
                list_for_each_entry(kvm, &vm_list, vm_list) {
                        kvm_for_each_vcpu(i, vcpu, kvm) {
                                if (vcpu->cpu != freq->cpu)
                                        continue;
                                if (vcpu->cpu != smp_processor_id())
                                       send_ipi++;
                                kvm_request_guest_time_update(vcpu);
                        }
                }
                spin_unlock(&kvm_lock);
                <--- a remote CPU could have updated kvmclock information
                     with stale cpu_tsc_khz, clearing the
                     KVM_REQ_KVMCLOCK_UPDATE bit.
                smp_call_function(evict) (which sets cpu_tsc_synchronized
                                          to zero)

Maybe worthwhile to unify it. Perhaps use the per cpu tsc generation in
addition to vcpu_load to update kvmclock info (on arch vcpu_load update
kvmclock store generation, update again on generation change).

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/