On Tue, Jul 21, 2020 at 8:26 PM Oliver Upton <oupton@xxxxxxxxxx> wrote:
>
> To date, VMMs have typically restored the guest's TSCs by value using
> the KVM_SET_MSRS ioctl for each vCPU. However, restoring the TSCs by
> value introduces some challenges with synchronization as the TSCs
> continue to tick throughout the restoration process. As such, KVM has
> some heuristics around TSC writes to infer whether or not the guest or
> host is attempting to synchronize the TSCs.
>
> Instead of guessing at the intentions of a VMM, it'd be better to
> provide an interface that allows for explicit synchronization of the
> guest's TSCs. To that end, this series introduces the
> KVM_{GET,SET}_TSC_OFFSET ioctls, yielding control of the TSC offset to
> userspace.
>
> v2 => v3:
> - Mark kvm_write_tsc_offset() as static (whoops)
>
> v1 => v2:
> - Added clarification to the documentation of KVM_SET_TSC_OFFSET to
> indicate that it can be used instead of an IA32_TSC MSR restore
> through KVM_SET_MSRS
> - Fixed KVM_SET_TSC_OFFSET to participate in the existing TSC
> synchronization heuristics, thereby enabling the KVM masterclock when
> all vCPUs are in phase.
>
> Oliver Upton (4):
> kvm: x86: refactor masterclock sync heuristics out of kvm_write_tsc
> kvm: vmx: check tsc offsetting with nested_cpu_has()
> selftests: kvm: use a helper function for reading cpuid
> selftests: kvm: introduce tsc_offset_test
>
> Peter Hornyack (1):
> kvm: x86: add KVM_{GET,SET}_TSC_OFFSET ioctls
>
> Documentation/virt/kvm/api.rst | 31 ++
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/vmx/vmx.c | 2 +-
> arch/x86/kvm/x86.c | 147 ++++---
> include/uapi/linux/kvm.h | 5 +
> tools/testing/selftests/kvm/.gitignore | 1 +
> tools/testing/selftests/kvm/Makefile | 1 +
> .../testing/selftests/kvm/include/test_util.h | 3 +
> .../selftests/kvm/include/x86_64/processor.h | 15 +
> .../selftests/kvm/include/x86_64/svm_util.h | 10 +-
> .../selftests/kvm/include/x86_64/vmx.h | 9 +
> tools/testing/selftests/kvm/lib/kvm_util.c | 1 +
> tools/testing/selftests/kvm/lib/x86_64/vmx.c | 11 +
> .../selftests/kvm/x86_64/tsc_offset_test.c | 362 ++++++++++++++++++
> 14 files changed, 550 insertions(+), 49 deletions(-)
> create mode 100644 tools/testing/selftests/kvm/x86_64/tsc_offset_test.c
>
> --
> 2.28.0.rc0.142.g3c755180ce-goog
>
Ping :)
