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    Subject[PATCH 4.19 094/105] KVM: lapic: Busy wait for timer to expire when using hv_timer
    Date
    From: Sean Christopherson <sean.j.christopherson@intel.com>

    commit ee66e453db13d4837a0dcf9d43efa7a88603161b upstream.

    ...now that VMX's preemption timer, i.e. the hv_timer, also adjusts its
    programmed time based on lapic_timer_advance_ns. Without the delay, a
    guest can see a timer interrupt arrive before the requested time when
    KVM is using the hv_timer to emulate the guest's interrupt.

    Fixes: c5ce8235cffa0 ("KVM: VMX: Optimize tscdeadline timer latency")
    Cc: <stable@vger.kernel.org>
    Cc: Wanpeng Li <wanpengli@tencent.com>
    Reviewed-by: Liran Alon <liran.alon@oracle.com>
    Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kvm/lapic.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/x86/kvm/lapic.c
    +++ b/arch/x86/kvm/lapic.c
    @@ -1449,7 +1449,7 @@ static void apic_timer_expired(struct kv
    if (swait_active(q))
    swake_up_one(q);

    - if (apic_lvtt_tscdeadline(apic))
    + if (apic_lvtt_tscdeadline(apic) || ktimer->hv_timer_in_use)
    ktimer->expired_tscdeadline = ktimer->tscdeadline;
    }


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