[pve-devel] [PATCH] kvm : fix stealtime bug

[Alexandre Derumier]

Signed-off-by: Alexandre Derumier <aderumier at odiso.com>
---
 Makefile           |   1 +
 kvmstealtime.patch | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 kvmstealtime.patch

diff --git a/Makefile b/Makefile
index 287585b..5818f32 100644
--- a/Makefile
+++ b/Makefile
@@ -209,6 +209,7 @@ ${KERNEL_SRC}/README ${KERNEL_CFG_ORG}: ${KERNELSRCTAR}
 	#cd ${KERNEL_SRC}; patch -p1 <../add-empty-ndo_poll_controller-to-veth.patch
 	#cd ${KERNEL_SRC}; patch -p1 <../override_for_missing_acs_capabilities.patch
 	#cd ${KERNEL_SRC}; patch -p1 <../vhost-net-extend-device-allocation-to-vmalloc.patch
+	#cd ${KERNEL_SRC}; patch -p1 <../kvmstealtime.patch
 	sed -i ${KERNEL_SRC}/Makefile -e 's/^EXTRAVERSION.*$$/EXTRAVERSION=${EXTRAVERSION}/'
 	touch $@
 
diff --git a/kvmstealtime.patch b/kvmstealtime.patch
new file mode 100644
index 0000000..ef1807a
--- /dev/null
+++ b/kvmstealtime.patch
@@ -0,0 +1,112 @@
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+Date:	Wed, 14 Oct 2015 19:33:09 -0300
+From:	Marcelo Tosatti <mtosatti at redhat.com>
+To:	kvm at vger.kernel.org
+Cc:	Rik van Riel <riel at redhat.com>,
+	"Dr. David Alan Gilbert" <dgilbert at redhat.com>,
+	Paolo Bonzini <pbonzini at redhat.com>,
+	Amit Shah <amit.shah at redhat.com>
+Subject: [PATCH] KVM: x86: move steal time initialization to vcpu entry time 
+Message-ID: <20151014223309.GA13900 at amt.cnet>
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+
+
+As reported at https://bugs.launchpad.net/qemu/+bug/1494350, 
+it is possible to have vcpu->arch.st.last_steal initialized 
+from a thread other than vcpu thread, say the iothread, via 
+KVM_SET_MSRS.
+
+Which can cause an overflow later (when subtracting from vcpu threads
+sched_info.run_delay).
+
+To avoid that, move steal time accumulation to vcpu entry time, 
+before copying steal time data to guest.
+
+Signed-off-by: Marcelo Tosatti <mtosatti at redhat.com>
+
+diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
+index 8f0f6ec..0e0332e 100644
+--- a/arch/x86/kvm/x86.c
++++ b/arch/x86/kvm/x86.c
+@@ -2030,6 +2030,8 @@ static void accumulate_steal_time(struct kvm_vcpu *vcpu)
+ 
+ static void record_steal_time(struct kvm_vcpu *vcpu)
+ {
++	accumulate_steal_time(vcpu);
++
+ 	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
+ 		return;
+ 
+@@ -2182,12 +2184,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+ 		if (!(data & KVM_MSR_ENABLED))
+ 			break;
+ 
+-		vcpu->arch.st.last_steal = current->sched_info.run_delay;
+-
+-		preempt_disable();
+-		accumulate_steal_time(vcpu);
+-		preempt_enable();
+-
+ 		kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
+ 
+ 		break;
+@@ -2830,7 +2826,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
+ 		vcpu->cpu = cpu;
+ 	}
+ 
+-	accumulate_steal_time(vcpu);
+ 	kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
+ }
+ 
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