Re: [RFC PATCH v3 16/21] KVM: x86: Factor out kvm_use_master_clock()

[Paul Durrant]

On 22/05/2024 01:17, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
>
> Both kvm_track_tsc_matching() and pvclock_update_vm_gtod_copy() make a
> decision about whether the KVM clock should be in master clock mode.
>
> They use *different* criteria for the decision though. This isn't really
> a problem; it only has the potential to cause unnecessary invocations of
> KVM_REQ_MASTERCLOCK_UPDATE if the masterclock was disabled due to TSC
> going backwards, or the guest using the old MSR. But it isn't pretty.
>
> Factor the decision out to a single function. And document the historical
> reason why it's disabled for guests that use the old MSR_KVM_SYSTEM_TIME.
>
> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> ---
>   arch/x86/kvm/x86.c | 27 +++++++++++++++++++++++----
>   1 file changed, 23 insertions(+), 4 deletions(-)

Reviewed-by: Paul Durrant <paul@xxxxxxx>