Re: [PATCH 05/10] KVM: x86: Explicitly disable TSC scaling without CONSTANT_TSC

[Paul Durrant <xadimgnik@gmail.com>]

On 18/04/2024 20:34, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> KVM does make an attempt to cope with non-constant TSC, and has notifiers
> to handle host TSC frequency changes. However, it *only* adjusts the KVM
> clock, and doesn't adjust TSC frequency scaling when the host changes.
> 
> This is presumably because non-constant TSCs were fixed in hardware long
> before TSC scaling was implemented, so there should never be real CPUs
> which have TSC scaling but *not* CONSTANT_TSC.
> 
> Such a combination could potentially happen in some odd L1 nesting
> environment, but it isn't worth trying to support it. Just make the
> dependency explicit.
> 
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>   arch/x86/kvm/svm/svm.c | 3 ++-
>   arch/x86/kvm/vmx/vmx.c | 2 +-
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 

Reviewed-by: Paul Durrant <paul@xen.org>