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KVM: x86: do not go through vcpu in __get_kvmclock_ns 

Going through the first VCPU is wrong if you follow a KVM_SET_CLOCK with
a KVM_GET_CLOCK immediately after, without letting the VCPU run and
call kvm_guest_time_update.

To fix this, compute the kvmclock value ourselves, using the master
clock (tsc, nsec) pair as the base and the host CPU frequency as
the scale.

Reported-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-11-16 18:31:30 +01:00 committed by Radim Krčmář
parent e5dbc4bf0b
commit 8b95344064
1 changed files with 13 additions and 8 deletions
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21
arch/x86/kvm/x86.c
View File

@ -1724,18 +1724,23 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
static u64 __get_kvmclock_ns(struct kvm *kvm)
{
struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, 0);
struct kvm_arch *ka = &kvm->arch;
s64 ns;
struct pvclock_vcpu_time_info hv_clock;
if (vcpu->arch.hv_clock.flags & PVCLOCK_TSC_STABLE_BIT) {
u64 tsc = kvm_read_l1_tsc(vcpu, rdtsc());
ns = __pvclock_read_cycles(&vcpu->arch.hv_clock, tsc);
} else {
ns = ktime_get_boot_ns() + ka->kvmclock_offset;
spin_lock(&ka->pvclock_gtod_sync_lock);
if (!ka->use_master_clock) {
spin_unlock(&ka->pvclock_gtod_sync_lock);
return ktime_get_boot_ns() + ka->kvmclock_offset;
}
return ns;
hv_clock.tsc_timestamp = ka->master_cycle_now;
hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;
spin_unlock(&ka->pvclock_gtod_sync_lock);
kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
&hv_clock.tsc_shift,
&hv_clock.tsc_to_system_mul);
return __pvclock_read_cycles(&hv_clock, rdtsc());
}
u64 get_kvmclock_ns(struct kvm *kvm)