From: Jack Allister <jalliste@amazon.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Sean Christopherson <seanjc@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>,
Paul Durrant <paul@xen.org>,
"Jack Allister" <jalliste@amazon.com>, <kvm@vger.kernel.org>,
<linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: [PATCH 0/2] Add API to correct KVM/PV clock drift
Date: Mon, 8 Apr 2024 22:07:02 +0000 [thread overview]
Message-ID: <20240408220705.7637-1-jalliste@amazon.com> (raw)
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
next reply other threads:[~2024-04-08 22:07 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-08 22:07 Jack Allister [this message]
2024-04-08 22:07 ` [PATCH 1/2] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for KVM clock drift fixup Jack Allister
2024-04-09 0:34 ` Dongli Zhang
2024-04-09 3:50 ` David Woodhouse
2024-04-10 10:08 ` Allister, Jack
2024-04-08 22:07 ` [PATCH 2/2] KVM: selftests: Add KVM/PV clock selftest to prove timer drift correction Jack Allister
2024-04-09 0:43 ` Dongli Zhang
2024-04-09 4:23 ` David Woodhouse
2024-04-10 10:15 ` Allister, Jack
2024-04-11 13:28 ` David Woodhouse
2024-04-19 17:13 ` Chen, Zide
[not found] ` <17F1A2E9-6BAD-40E7-ACDD-B110CFC124B3@infradead.org>
2024-04-19 18:43 ` David Woodhouse
2024-04-19 23:54 ` Chen, Zide
2024-04-20 10:32 ` David Woodhouse
2024-04-20 16:03 ` David Woodhouse
2024-04-22 22:02 ` Chen, Zide
2024-04-23 7:49 ` David Woodhouse
2024-04-23 17:59 ` Chen, Zide
2024-04-23 21:02 ` David Woodhouse
2024-04-24 12:58 ` David Woodhouse
2024-04-19 19:34 ` David Woodhouse
2024-04-19 23:53 ` Chen, Zide
2024-04-10 9:52 ` [PATCH v2 0/2] Add API for accurate KVM/PV clock migration Jack Allister
2024-04-10 9:52 ` [PATCH v2 1/2] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for accurate KVM " Jack Allister
2024-04-10 10:29 ` Paul Durrant
2024-04-10 12:09 ` David Woodhouse
2024-04-10 12:43 ` Paul Durrant
2024-04-17 19:50 ` David Woodhouse
2024-04-15 7:16 ` David Woodhouse
2024-04-10 9:52 ` [PATCH v2 2/2] KVM: selftests: Add KVM/PV clock selftest to prove timer correction Jack Allister
2024-04-10 10:36 ` Paul Durrant
2024-04-12 8:19 ` Dongli Zhang
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