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KVM: x86: limit difference between kvmclock updates 

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.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
This commit is contained in:
Marcelo Tosatti 2013-05-09 20:21:41 -03:00 committed by Gleb Natapov
parent f1ed0450a5
commit 0061d53daf
2 changed files with 29 additions and 2 deletions
arch/x86/kvm
x86.c
include/linux
kvm_host.h

30
arch/x86/kvm/x86.c
View File

@ -1588,6 +1588,30 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
return 0; 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) static bool msr_mtrr_valid(unsigned msr)
{ {
switch (msr) { switch (msr) {
@ -1985,7 +2009,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
kvmclock_reset(vcpu); kvmclock_reset(vcpu);
vcpu->arch.time = data; 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... */ /* we verify if the enable bit is set... */
if (!(data & 1)) if (!(data & 1))
@ -2702,7 +2726,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
* kvmclock on vcpu->cpu migration * kvmclock on vcpu->cpu migration
*/ */
if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) 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) if (vcpu->cpu != cpu)
kvm_migrate_timers(vcpu); kvm_migrate_timers(vcpu);
vcpu->cpu = cpu; vcpu->cpu = cpu;
@ -5703,6 +5727,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
__kvm_migrate_timers(vcpu); __kvm_migrate_timers(vcpu);
if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu)) if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu))
kvm_gen_update_masterclock(vcpu->kvm); 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)) { if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) {
r = kvm_guest_time_update(vcpu); r = kvm_guest_time_update(vcpu);
if (unlikely(r)) if (unlikely(r))

1
include/linux/kvm_host.h
View File

@ -124,6 +124,7 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQ_MCLOCK_INPROGRESS 19 #define KVM_REQ_MCLOCK_INPROGRESS 19
#define KVM_REQ_EPR_EXIT 20 #define KVM_REQ_EPR_EXIT 20
#define KVM_REQ_SCAN_IOAPIC 21 #define KVM_REQ_SCAN_IOAPIC 21
#define KVM_REQ_GLOBAL_CLOCK_UPDATE 22
#define KVM_USERSPACE_IRQ_SOURCE_ID 0 #define KVM_USERSPACE_IRQ_SOURCE_ID 0
#define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1 #define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1