When KVM_CAP_ADJUST_CLOCK is passed to KVM_CHECK_EXTENSION, it returns the
set of bits that KVM can return in struct kvm_clock_data's flag member.
-The only flag defined now is KVM_CLOCK_TSC_STABLE. If set, the returned
-value is the exact kvmclock value seen by all VCPUs at the instant
-when KVM_GET_CLOCK was called. If clear, the returned value is simply
-CLOCK_MONOTONIC plus a constant offset; the offset can be modified
-with KVM_SET_CLOCK. KVM will try to make all VCPUs follow this clock,
-but the exact value read by each VCPU could differ, because the host
-TSC is not stable.
+The following flags are defined:
+
+KVM_CLOCK_TSC_STABLE
+ If set, the returned value is the exact kvmclock
+ value seen by all VCPUs at the instant when KVM_GET_CLOCK was called.
+ If clear, the returned value is simply CLOCK_MONOTONIC plus a constant
+ offset; the offset can be modified with KVM_SET_CLOCK. KVM will try
+ to make all VCPUs follow this clock, but the exact value read by each
+ VCPU could differ, because the host TSC is not stable.
+
+KVM_CLOCK_REALTIME
+ If set, the `realtime` field in the kvm_clock_data
+ structure is populated with the value of the host's real time
+ clocksource at the instant when KVM_GET_CLOCK was called. If clear,
+ the `realtime` field does not contain a value.
+
+KVM_CLOCK_HOST_TSC
+ If set, the `host_tsc` field in the kvm_clock_data
+ structure is populated with the value of the host's timestamp counter (TSC)
+ at the instant when KVM_GET_CLOCK was called. If clear, the `host_tsc` field
+ does not contain a value.
::
struct kvm_clock_data {
__u64 clock; /* kvmclock current value */
__u32 flags;
- __u32 pad[9];
+ __u32 pad0;
+ __u64 realtime;
+ __u64 host_tsc;
+ __u32 pad[4];
};
In conjunction with KVM_GET_CLOCK, it is used to ensure monotonicity on scenarios
such as migration.
+The following flags can be passed:
+
+KVM_CLOCK_REALTIME
+ If set, KVM will compare the value of the `realtime` field
+ with the value of the host's real time clocksource at the instant when
+ KVM_SET_CLOCK was called. The difference in elapsed time is added to the final
+ kvmclock value that will be provided to guests.
+
+Other flags returned by ``KVM_GET_CLOCK`` are accepted but ignored.
+
::
struct kvm_clock_data {
__u64 clock; /* kvmclock current value */
__u32 flags;
- __u32 pad[9];
+ __u32 pad0;
+ __u64 realtime;
+ __u64 host_tsc;
+ __u32 pad[4];
};
struct pvclock_vcpu_time_info hv_clock;
unsigned long flags;
+ data->flags = 0;
spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags);
if (!ka->use_master_clock) {
spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags);
get_cpu();
if (__this_cpu_read(cpu_tsc_khz)) {
+#ifdef CONFIG_X86_64
+ struct timespec64 ts;
+
+ if (kvm_get_walltime_and_clockread(&ts, &data->host_tsc)) {
+ data->realtime = ts.tv_nsec + NSEC_PER_SEC * ts.tv_sec;
+ data->flags |= KVM_CLOCK_REALTIME | KVM_CLOCK_HOST_TSC;
+ } else
+#endif
+ data->host_tsc = rdtsc();
+
kvm_get_time_scale(NSEC_PER_SEC, __this_cpu_read(cpu_tsc_khz) * 1000LL,
&hv_clock.tsc_shift,
&hv_clock.tsc_to_system_mul);
- data->clock = __pvclock_read_cycles(&hv_clock, rdtsc());
+ data->clock = __pvclock_read_cycles(&hv_clock, data->host_tsc);
} else {
data->clock = get_kvmclock_base_ns() + ka->kvmclock_offset;
}
{
struct kvm_clock_data data;
- /*
- * Zero flags as it's accessed RMW, leave everything else uninitialized
- * as clock is always written and no other fields are consumed.
- */
- data.flags = 0;
-
get_kvmclock(kvm, &data);
return data.clock;
}
r = KVM_SYNC_X86_VALID_FIELDS;
break;
case KVM_CAP_ADJUST_CLOCK:
- r = KVM_CLOCK_TSC_STABLE;
+ r = KVM_CLOCK_VALID_FLAGS;
break;
case KVM_CAP_X86_DISABLE_EXITS:
r |= KVM_X86_DISABLE_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
{
struct kvm_arch *ka = &kvm->arch;
struct kvm_clock_data data;
- u64 now_ns;
+ u64 now_raw_ns;
if (copy_from_user(&data, argp, sizeof(data)))
return -EFAULT;
- if (data.flags)
+ /*
+ * Only KVM_CLOCK_REALTIME is used, but allow passing the
+ * result of KVM_GET_CLOCK back to KVM_SET_CLOCK.
+ */
+ if (data.flags & ~KVM_CLOCK_VALID_FLAGS)
return -EINVAL;
kvm_hv_invalidate_tsc_page(kvm);
* is slightly ahead) here we risk going negative on unsigned
* 'system_time' when 'data.clock' is very small.
*/
- if (kvm->arch.use_master_clock)
- now_ns = ka->master_kernel_ns;
+ if (data.flags & KVM_CLOCK_REALTIME) {
+ u64 now_real_ns = ktime_get_real_ns();
+
+ /*
+ * Avoid stepping the kvmclock backwards.
+ */
+ if (now_real_ns > data.realtime)
+ data.clock += now_real_ns - data.realtime;
+ }
+
+ if (ka->use_master_clock)
+ now_raw_ns = ka->master_kernel_ns;
else
- now_ns = get_kvmclock_base_ns();
- ka->kvmclock_offset = data.clock - now_ns;
+ now_raw_ns = get_kvmclock_base_ns();
+ ka->kvmclock_offset = data.clock - now_raw_ns;
kvm_end_pvclock_update(kvm);
return 0;
}
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