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Date: Thu, 5 Oct 2017 18:54:25 -0700 From: Wanpeng Li <kernellwp@...il.com> To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org Cc: Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com>, Wanpeng Li <wanpeng.li@...mail.com> Subject: [PATCH v6 2/3] KVM: LAPIC: Keep timer running when switching between one-shot and periodic mode From: Wanpeng Li <wanpeng.li@...mail.com> If we take TSC-deadline mode timer out of the picture, the Intel SDM does not say that the timer is disable when the timer mode is change, either from one-shot to periodic or vice versa. After this patch, the timer is no longer disarmed on change of mode, so the counter (TMCCT) keeps counting down. So what does a write to LVTT changes ? On baremetal, the change of mode is probably taken into account only when the counter reach 0. When this happen, LVTT is use to figure out if the counter should restard counting down from TMICT (so periodic mode) or stop counting (if one-shot mode). This patch is based on observation of the behavior of the APIC timer on baremetal as well as check that they does not go against the description written in the Intel SDM. Cc: Paolo Bonzini <pbonzini@...hat.com> Cc: Radim Krčmář <rkrcmar@...hat.com> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com> --- arch/x86/kvm/lapic.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 8841bb5..14f63b3 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1329,10 +1329,14 @@ static void apic_update_lvtt(struct kvm_lapic *apic) if (apic->lapic_timer.timer_mode != timer_mode) { if (apic_lvtt_tscdeadline(apic) != (timer_mode == - APIC_LVT_TIMER_TSCDEADLINE)) + APIC_LVT_TIMER_TSCDEADLINE)) { kvm_lapic_set_reg(apic, APIC_TMICT, 0); + hrtimer_cancel(&apic->lapic_timer.timer); + } + if (apic_lvtt_oneshot(apic) && (timer_mode == + APIC_LVT_TIMER_PERIODIC)) + limit_periodic_timer_frequency(apic); apic->lapic_timer.timer_mode = timer_mode; - hrtimer_cancel(&apic->lapic_timer.timer); } } -- 2.7.4
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