[Devel] [PATCH RHEL7 COMMIT] ms/KVM: x86: handle 0 write to TSC_DEADLINE MSR

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-862.9.1.vz7.63.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-862.9.1.vz7.63.2
------>
commit 1c0144891eb662261fdabb55649c0250c5c0df95
Author: Radim Krčmář <rkrcmar at redhat.com>
Date:   Wed Jul 25 18:47:09 2018 +0300

    ms/KVM: x86: handle 0 write to TSC_DEADLINE MSR
    
    0 should disable the timer, but start_hv_timer will recognize it as an
    expired timer instead.
    
    Signed-off-by: Radim Krčmář <rkrcmar at redhat.com>
    Reviewed-by: Wanpeng Li <wanpeng.li at hotmail.com>
    Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
    (cherry picked from commit 86bbc1e6d7ce016f1b2e8c29864cd7b75b00ff96)
    Signed-off-by: Viktor Prutyanov <viktor.prutyanov at virtuozzo.com>
    
    https://jira.sw.ru/browse/PSBM-86578
    
    Signed-off-by: Viktor Prutyanov <viktor.prutyanov at virtuozzo.com>
    
    =====================
    Patchset description:
    
    Fix guest context switch performance degradation.
    
    https://jira.sw.ru/browse/PSBM-86578
    
    Following patches were adopted from mainline kernel to fix guest Windows
    context switch performance degradation.
    
    VMX preemption timer support was added in kernel-3.10.0-862.3.2.el7. In this
    case, timer incorrectly triggers despite of its disabling and causes extra
    VMexit on every context switch. These patches add correct handling of disabled
    timer.
    
    Radim Krčmář (3):
      KVM: x86: handle 0 write to TSC_DEADLINE MSR
      KVM: x86: really disarm lapic timer when clearing TMICT
      KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch
    
    Wanpeng Li (3):
      KVM: LAPIC: Fix lapic timer mode transition
      KVM: LAPIC: Introduce limit_periodic_timer_frequency
      KVM: LAPIC: Keep timer running when switching between one-shot and
        periodic mode
---
 arch/x86/kvm/lapic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index f16f16413992..4fb6d073a8ce 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1526,6 +1526,9 @@ static bool start_hv_timer(struct kvm_lapic *apic)
 	if (!apic_lvtt_period(apic) && atomic_read(&ktimer->pending))
 		return false;
 
+	if (!ktimer->tscdeadline)
+		return false;
+
 	r = kvm_x86_ops->set_hv_timer(apic->vcpu, ktimer->tscdeadline);
 	if (r < 0)
 		return false;