2017-10-06 7:14 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>: > 2017-10-06 2:14 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >> 2017-10-05 07:35-0700, Wanpeng Li: >>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>> >>> 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 <pbonzini@xxxxxxxxxx> >>> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> >>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>> --- >>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c >>> @@ -1474,9 +1474,24 @@ static bool set_target_expiration(struct kvm_lapic *apic) >>> ktime_to_ns(ktime_add_ns(now, >>> apic->lapic_timer.period))); >>> >>> + delta = apic->lapic_timer.period; >>> + if (apic->divide_count != old_divisor) { >> >> Hm, nothing should happen if the guest writes the same value TDCR, but >> we'll reset the timer. (An extra argument would solve it, but maybe it >> would be nicer to add a new function for updating the expiration.) > > Agreed. > >> >>> + remaining = ktime_sub(apic->lapic_timer.target_expiration, now); >>> + if (ktime_to_ns(remaining) < 0) >>> + remaining = 0; >>> + delta = mod_64(ktime_to_ns(remaining), apic->lapic_timer.period); >>> + >>> + if (!delta) >>> + return false; >>> + >>> + apic->lapic_timer.period = (u64)kvm_lapic_get_reg(apic, APIC_TMICT) >>> + * APIC_BUS_CYCLE_NS * apic->divide_count; >> >> I'd prefer to apply the rate limiting (done earlier in this function) to >> the period. This version allows the guest to configure 128 times more >> frequent interrupts in the host. >> (And thinking about it, the version of [2/3] I proposed has similar >> problem when switching from one-shot to periodic, only there it is >> unpredictably limited by the speed of KVM.) > > We didn't stop and restart the timer, why the rate will influence us for [2/3]? Have already done in v6, please have a review. :) Regards, Wanpeng Li >> >> Thanks. >> >>> + delta = delta * apic->divide_count / old_divisor; >>> + } >>> + >>> apic->lapic_timer.tscdeadline = kvm_read_l1_tsc(apic->vcpu, tscl) + >>> - nsec_to_cycles(apic->vcpu, apic->lapic_timer.period); >>> - apic->lapic_timer.target_expiration = ktime_add_ns(now, apic->lapic_timer.period); >>> + nsec_to_cycles(apic->vcpu, delta); >>> + apic->lapic_timer.target_expiration = ktime_add_ns(now, delta); >>> >>> return true; >>> }