linux-kernel - [PATCH 3.10 44/53] KVM: x86: update masterclock values on TSC writes

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Message-Id: <20150304054617.287760726@linuxfoundation.org>
Date:	Tue,  3 Mar 2015 22:06:47 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 3.10 44/53] KVM: x86: update masterclock values on TSC writes

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Marcelo Tosatti <mtosatti@...hat.com>

commit 7f187922ddf6b67f2999a76dcb71663097b75497 upstream.

When the guest writes to the TSC, the masterclock TSC copy must be
updated as well along with the TSC_OFFSET update, otherwise a negative
tsc_timestamp is calculated at kvm_guest_time_update.

Once "if (!vcpus_matched && ka->use_master_clock)" is simplified to
"if (ka->use_master_clock)", the corresponding "if (!ka->use_master_clock)"
becomes redundant, so remove the do_request boolean and collapse
everything into a single condition.

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kvm/x86.c |   19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1182,21 +1182,22 @@ void kvm_track_tsc_matching(struct kvm_v
 {
 #ifdef CONFIG_X86_64
 	bool vcpus_matched;
-	bool do_request = false;
 	struct kvm_arch *ka = &vcpu->kvm->arch;
 	struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
 
 	vcpus_matched = (ka->nr_vcpus_matched_tsc + 1 ==
 			 atomic_read(&vcpu->kvm->online_vcpus));
 
-	if (vcpus_matched && gtod->clock.vclock_mode == VCLOCK_TSC)
-		if (!ka->use_master_clock)
-			do_request = 1;
-
-	if (!vcpus_matched && ka->use_master_clock)
-			do_request = 1;
-
-	if (do_request)
+	/*
+	 * Once the masterclock is enabled, always perform request in
+	 * order to update it.
+	 *
+	 * In order to enable masterclock, the host clocksource must be TSC
+	 * and the vcpus need to have matched TSCs.  When that happens,
+	 * perform request to enable masterclock.
+	 */
+	if (ka->use_master_clock ||
+	    (gtod->clock.vclock_mode == VCLOCK_TSC && vcpus_matched))
 		kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
 
 	trace_kvm_track_tsc(vcpu->vcpu_id, ka->nr_vcpus_matched_tsc,


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