diff options
| author | Oliver Upton <oupton@google.com> | 2021-09-16 18:15:38 +0000 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2021-10-18 14:43:45 -0400 |
| commit | 828ca89628bfcb1b8f27535025f69dd00eb55207 (patch) | |
| tree | 5197c686cff8825d4f994c864986a97bfa67b5aa /arch/x86/include/uapi/asm/kvm.h | |
| parent | 58d4277be9b66d8048054c8e57214a86b6b15da9 (diff) | |
KVM: x86: Expose TSC offset controls to userspace
To date, VMM-directed TSC synchronization and migration has been a bit
messy. KVM has some baked-in heuristics around TSC writes to infer if
the VMM is attempting to synchronize. This is problematic, as it depends
on host userspace writing to the guest's TSC within 1 second of the last
write.
A much cleaner approach to configuring the guest's views of the TSC is to
simply migrate the TSC offset for every vCPU. Offsets are idempotent,
and thus not subject to change depending on when the VMM actually
reads/writes values from/to KVM. The VMM can then read the TSC once with
KVM_GET_CLOCK to capture a (realtime, host_tsc) pair at the instant when
the guest is paused.
Cc: David Matlack <dmatlack@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210916181538.968978-8-oupton@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/include/uapi/asm/kvm.h')
| -rw-r--r-- | arch/x86/include/uapi/asm/kvm.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h index 2ef1f6513c68..5a776a08f78c 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -504,4 +504,8 @@ struct kvm_pmu_event_filter { #define KVM_PMU_EVENT_ALLOW 0 #define KVM_PMU_EVENT_DENY 1 +/* for KVM_{GET,SET,HAS}_DEVICE_ATTR */ +#define KVM_VCPU_TSC_CTRL 0 /* control group for the timestamp counter (TSC) */ +#define KVM_VCPU_TSC_OFFSET 0 /* attribute for the TSC offset */ + #endif /* _ASM_X86_KVM_H */ |