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KVM: x86: Report host tsc and realtime values in KVM_GET_CLOCK

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Handling the migration of TSCs correctly is difficult, in part because
Linux does not provide userspace with the ability to retrieve a (TSC,
realtime) clock pair for a single instant in time. In lieu of a more
convenient facility, KVM can report similar information in the kvm_clock
structure.

Provide userspace with a host TSC & realtime pair iff the realtime clock
is based on the TSC. If userspace provides KVM_SET_CLOCK with a valid
realtime value, advance the KVM clock by the amount of elapsed time. Do
not step the KVM clock backwards, though, as it is a monotonic
oscillator.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210916181538.968978-5-oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Oliver Upton 2021-09-16 18:15:35 +00:00 • committed by Paolo Bonzini
parent 3d5e7a28b1
commit c68dc1b577
4 changed files with 81 additions and 24 deletions
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7
include/uapi/linux/kvm.h
View file

@ -1231,11 +1231,16 @@ struct kvm_irqfd {
/* Do not use 1, KVM_CHECK_EXTENSION returned it before we had flags. */
#define KVM_CLOCK_TSC_STABLE 2
#define KVM_CLOCK_REALTIME (1 << 2)
#define KVM_CLOCK_HOST_TSC (1 << 3)
struct kvm_clock_data {
__u64 clock;
__u32 flags;
__u32 pad[9];
__u32 pad0;
__u64 realtime;
__u64 host_tsc;
__u32 pad[4];
};
/* For KVM_CAP_SW_TLB */