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KVM: x86: add KVM_HC_CLOCK_PAIRING hypercall

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Add a hypercall to retrieve the host realtime clock and the TSC value
used to calculate that clock read.

Used to implement clock synchronization between host and guest.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Marcelo Tosatti
2017-01-24 15:09:39 -02:00
committed by Paolo Bonzini
parent 6342c50ad1
commit 55dd00a73a
4 changed files with 112 additions and 0 deletions
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35
Documentation/virtual/kvm/hypercalls.txt
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@@ -81,3 +81,38 @@ the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the
same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
is used in the hypercall for future use.
6. KVM_HC_CLOCK_PAIRING
------------------------
Architecture: x86
Status: active
Purpose: Hypercall used to synchronize host and guest clocks.
Usage:
a0: guest physical address where host copies
"struct kvm_clock_offset" structure.
a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0)
is supported (corresponding to the host's CLOCK_REALTIME clock).
struct kvm_clock_pairing {
__s64 sec;
__s64 nsec;
__u64 tsc;
__u32 flags;
__u32 pad[9];
};
Where:
* sec: seconds from clock_type clock.
* nsec: nanoseconds from clock_type clock.
* tsc: guest TSC value used to calculate sec/nsec pair
* flags: flags, unused (0) at the moment.
The hypercall lets a guest compute a precise timestamp across
host and guest. The guest can use the returned TSC value to
compute the CLOCK_REALTIME for its clock, at the same instant.
Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource,
or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK.