[focal:linux-azure/eoan:linux-azure][PATCH 0/2] LP#1875467: Enable invariant TSC support

[Kelsey Skunberg]

BugLink: http://bugs.launchpad.net/bugs/1875467

Microsoft would like to request two commits in all releases supported on
Azure. These commits benefit SAP workloads.

These requested commits will enable support for Invariant TSC in Linux
guest VMs. The invariant TSC means that the TSC continues at a fixed
rate regardless of the C-state or frequency of the processor (as long as
the processor remains in the ACPI S0 state).

These patches will allow guests to access the
HvSyntheticInvariantTscControl MSR and set bit 0 of this synthetic MSR,
which then enables the InvariantTSC feature. After setting the synthetic
MSR, CPUID will enumerate support for InvariantTSC.

The following two commits enable support:
9e0333ae38ee ("clocksource/drivers/hyper-v: Set TSC clocksource as
default w/ InvariantTSC")
dce7cd62754b ("x86/hyperv: Allow guests to enable InvariantTSC")

Clean cherry-pick for both commits.

Andrea Parri (2):
  x86/hyperv: Allow guests to enable InvariantTSC
  clocksource/drivers/hyper-v: Set TSC clocksource as default w/
    InvariantTSC

 arch/x86/include/asm/hyperv-tlfs.h |  5 +++++
 arch/x86/kernel/cpu/mshyperv.c     |  7 ++++++-
 drivers/clocksource/hyperv_timer.c | 12 ++++++++++--
 3 files changed, 21 insertions(+), 3 deletions(-)

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2.25.1