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[PATCH 3.10 09/18] KVM: x86: move steal time initialization to vcpu entry time

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

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

From: Marcelo Tosatti <mtosatti@redhat.com>

commit 7cae2bedcbd4680b155999655e49c27b9cf020fa upstream.

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@redhat.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kvm/x86.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1941,6 +1941,8 @@ static void accumulate_steal_time(struct
 
 static void record_steal_time(struct kvm_vcpu *vcpu)
 {
+	accumulate_steal_time(vcpu);
+
 	if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
 		return;
 
@@ -2074,12 +2076,6 @@ int kvm_set_msr_common(struct kvm_vcpu *
 		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;
@@ -2758,7 +2754,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu
 		vcpu->cpu = cpu;
 	}
 
-	accumulate_steal_time(vcpu);
 	kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
 }
 

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[PATCH 3.10 00/18] 3.10.101-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:00 +0100
  [PATCH 3.10 09/18] KVM: x86: move steal time initialization to vcpu entry time Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:00 +0100
  [PATCH 3.10 02/18] tracing: Fix check for cpu online when event is disabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:00 +0100
  [PATCH 3.10 04/18] ASoC: wm8958: Fix enum ctl accesses in a wrong type Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:00 +0100
  [PATCH 3.10 08/18] powerpc: Fix dedotify for binutils >= 2.26 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:00 +0100
  [PATCH 3.10 06/18] mac80211: fix use of uninitialised values in RX aggregation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:00 +0100
  [PATCH 3.10 18/18] Revert: "crypto: af_alg - Disallow bind/setkey/... after accept(2)" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:00 +0100
  [PATCH 3.10 13/18] efi: Make our variable validation list include the guid Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 3.10 12/18] efi: Do variable name validation tests in utf8 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 3.10 11/18] efi: Use ucs2_as_utf8 in efivarfs instead of open coding a bad version Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 3.10 14/18] efi: Make efivarfs entries immutable by default Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 3.10 10/18] lib/ucs2_string: Add ucs2 -> utf8 helper functions Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 3.10 15/18] efi: Add pstore variables to the deletion whitelist Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  Re: [PATCH 3.10 00/18] 3.10.101-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2016-03-15 00:20 +0100
  Re: [PATCH 3.10 00/18] 3.10.101-stable review Guenter Roeck <linux@roeck-us.net> - 2016-03-15 03:40 +0100
  Re: [PATCH 3.10 00/18] 3.10.101-stable review Guenter Roeck <linux@roeck-us.net> - 2016-03-16 04:10 +0100
    Re: [PATCH 3.10 00/18] 3.10.101-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-16 05:20 +0100

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