From c301b909e4b94e6395251787e28b335c51309fff Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Fri, 6 Oct 2017 07:38:32 -0700 Subject: [PATCH] KVM: LAPIC: Apply change to TDCR right away to the timer MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The description in the Intel SDM of how the divide configuration register is used: "The APIC timer frequency will be the processor's bus clock or core crystal clock frequency divided by the value specified in the divide configuration register." Observation of baremetal shown that when the TDCR is change, the TMCCT does not change or make a big jump in value, but the rate at which it count down change. The patch update the emulation to APIC timer to so that a change to the divide configuration would be reflected in the value of the counter and when the next interrupt is triggered. Cc: Paolo Bonzini Cc: Radim Krčmář Signed-off-by: Wanpeng Li [Fixed some whitespace and added a check for negative delta and running timer. - Radim] Signed-off-by: Radim Krčmář --- arch/x86/kvm/lapic.c | 36 ++++++++++++++++++++++++++++++++++-- 1 file changed, 34 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index f7ad11255557..2c9e88a82738 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -1456,6 +1456,30 @@ static void start_sw_period(struct kvm_lapic *apic) HRTIMER_MODE_ABS_PINNED); } +static void update_target_expiration(struct kvm_lapic *apic, uint32_t old_divisor) +{ + ktime_t now, remaining; + u64 ns_remaining_old, ns_remaining_new; + + apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT) + * APIC_BUS_CYCLE_NS * apic->divide_count; + limit_periodic_timer_frequency(apic); + + now = ktime_get(); + remaining = ktime_sub(apic->lapic_timer.target_expiration, now); + if (ktime_to_ns(remaining) < 0) + remaining = 0; + + ns_remaining_old = ktime_to_ns(remaining); + ns_remaining_new = mul_u64_u32_div(ns_remaining_old, + apic->divide_count, old_divisor); + + apic->lapic_timer.tscdeadline += + nsec_to_cycles(apic->vcpu, ns_remaining_new) - + nsec_to_cycles(apic->vcpu, ns_remaining_old); + apic->lapic_timer.target_expiration = ktime_add_ns(now, ns_remaining_new); +} + static bool set_target_expiration(struct kvm_lapic *apic) { ktime_t now; @@ -1748,13 +1772,21 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val) start_apic_timer(apic); break; - case APIC_TDCR: + case APIC_TDCR: { + uint32_t old_divisor = apic->divide_count; + if (val & 4) apic_debug("KVM_WRITE:TDCR %x\n", val); kvm_lapic_set_reg(apic, APIC_TDCR, val); update_divide_count(apic); + if (apic->divide_count != old_divisor && + apic->lapic_timer.period) { + hrtimer_cancel(&apic->lapic_timer.timer); + update_target_expiration(apic, old_divisor); + restart_apic_timer(apic); + } break; - + } case APIC_ESR: if (apic_x2apic_mode(apic) && val != 0) { apic_debug("KVM_WRITE:ESR not zero %x\n", val); -- 2.30.2