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author | Marcelo Tosatti <mtosatti@redhat.com> | 2017-01-24 15:09:39 -0200 |
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committer | Paolo Bonzini <pbonzini@redhat.com> | 2017-02-07 18:16:45 +0100 |
commit | 55dd00a73a518281bc846dc5de1a718349431eb2 (patch) | |
tree | 13c912f125578744049bf28902e26e5e30b57b66 /Documentation/virtual | |
parent | 6342c50ad12e8ce0736e722184a7dbdea4a3477f (diff) | |
download | linux-55dd00a73a518281bc846dc5de1a718349431eb2.tar.gz linux-55dd00a73a518281bc846dc5de1a718349431eb2.tar.bz2 linux-55dd00a73a518281bc846dc5de1a718349431eb2.zip |
KVM: x86: add KVM_HC_CLOCK_PAIRING hypercall
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>
Diffstat (limited to 'Documentation/virtual')
-rw-r--r-- | Documentation/virtual/kvm/hypercalls.txt | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/hypercalls.txt b/Documentation/virtual/kvm/hypercalls.txt index c8d040e27046..feaaa634f154 100644 --- a/Documentation/virtual/kvm/hypercalls.txt +++ b/Documentation/virtual/kvm/hypercalls.txt @@ -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. |