Messages in this thread | | | From | Jack Allister <> | Subject | [PATCH 0/2] Add API to correct KVM/PV clock drift | Date | Mon, 8 Apr 2024 22:07:02 +0000 |
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Guest VMs can be provided with a para-virtualized clock source to perform timekeeping. A KVM guest can map in a PV clock via the MSR_KVM_SYSTEM_TIME/MSR_KVM_SYSTEM_TIME_NEW virtualized MSRs. Where as on a Xen guest this can be provided via the vcpu/shared info pages.
These PV clocks both use a common structure which is mapped between host <-> guest to provide the PVTI (paravirtual time information) for the clock. This reference information is a guest TSC timestamp and a host system time at a SINGULAR point in time.
If KVM decides to update the reference information due to a KVM_REQ_MASTERCLOCK_UPDATE, a drift between the guest TSC and the PV clock can be observed, this is exascerbated when the guest TSC is also scaled too.
If the reference guest TSC & system time within the structure stay the same there is no potential for a drift between the TSC and PV clock.
This series adds in two patches, one to add in API/ioctl to allow a VMM to perform a correction/fixup of the PVTI structure when it knows that KVM may have updated the KVM clock information and a second one to verify that the drift is present & corrected.
Jack Allister (2): KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for KVM clock drift fixup KVM: selftests: Add KVM/PV clock selftest to prove timer drift correction
Documentation/virt/kvm/api.rst | 43 ++++ arch/x86/kvm/x86.c | 87 +++++++ include/uapi/linux/kvm.h | 3 + tools/testing/selftests/kvm/Makefile | 1 + .../selftests/kvm/x86_64/pvclock_test.c | 223 ++++++++++++++++++ 5 files changed, 357 insertions(+) create mode 100644 tools/testing/selftests/kvm/x86_64/pvclock_test.c
base-commit: 8cb4a9a82b21623dbb4b3051dd30d98356cf95bc -- 2.40.1
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