On Thu, May 09, 2013 at 08:21:41PM -0300, Marcelo Tosatti wrote:
>
> kvmclock updates which are isolated to a given vcpu, such as vcpu->cpu
> migration, should not allow system_timestamp from the rest of the vcpus
> to remain static. Otherwise ntp frequency correction applies to one
> vcpu's system_timestamp but not the others.
>
> So in those cases, request a kvmclock update for all vcpus. The worst
> case for a remote vcpu to update its kvmclock is then bounded by maximum
> nohz sleep latency.
>
Does this mean that when one vcpu is migrated all others are kicked out
from a guest mode?
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 94f35d2..a37cadc 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1569,6 +1569,30 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> return 0;
> }
>
> +/*
> + * kvmclock updates which are isolated to a given vcpu, such as
> + * vcpu->cpu migration, should not allow system_timestamp from
> + * the rest of the vcpus to remain static. Otherwise ntp frequency
> + * correction applies to one vcpu's system_timestamp but not
> + * the others.
> + *
> + * So in those cases, request a kvmclock update for all vcpus.
> + * The worst case for a remote vcpu to update its kvmclock
> + * is then bounded by maximum nohz sleep latency.
> + */
> +
> +static void kvm_gen_kvmclock_update(struct kvm_vcpu *v)
> +{
> + int i;
> + struct kvm *kvm = v->kvm;
> + struct kvm_vcpu *vcpu;
> +
> + kvm_for_each_vcpu(i, vcpu, kvm) {
> + set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests);
> + kvm_vcpu_kick(vcpu);
> + }
> +}
> +
> static bool msr_mtrr_valid(unsigned msr)
> {
> switch (msr) {
> @@ -1965,7 +1989,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> kvmclock_reset(vcpu);
>
> vcpu->arch.time = data;
> - kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
> + kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
>
> /* we verify if the enable bit is set... */
> if (!(data & 1))
> @@ -2684,7 +2708,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> * kvmclock on vcpu->cpu migration
> */
> if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1)
> - kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
> + kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
> if (vcpu->cpu != cpu)
> kvm_migrate_timers(vcpu);
> vcpu->cpu = cpu;
> @@ -5704,6 +5728,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> __kvm_migrate_timers(vcpu);
> if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu))
> kvm_gen_update_masterclock(vcpu->kvm);
> + if (kvm_check_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu))
> + kvm_gen_kvmclock_update(vcpu);
> if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) {
> r = kvm_guest_time_update(vcpu);
> if (unlikely(r))
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 7823b63..044b0b9 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -126,6 +126,7 @@ static inline bool is_error_page(struct page *page)
> #define KVM_REQ_MCLOCK_INPROGRESS 19
> #define KVM_REQ_EPR_EXIT 20
> #define KVM_REQ_SCAN_IOAPIC 21
> +#define KVM_REQ_GLOBAL_CLOCK_UPDATE 22
>
> #define KVM_USERSPACE_IRQ_SOURCE_ID 0
> #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
> --
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--
Gleb.
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