Re: [PATCH 0/8] KVM: VMX: Implement nested TSC scaling

[Maxim Levitsky <mlevitsk@redhat.com>]

On Thu, 2021-05-06 at 17:48 +0000, Stamatis, Ilias wrote:
> On Thu, 2021-05-06 at 10:16 -0700, Jim Mattson wrote:
> > On Thu, May 6, 2021 at 3:34 AM <ilstam@mailbox.org> wrote:
> > > From: Ilias Stamatis <ilstam@amazon.com>
> > > 
> > > KVM currently supports hardware-assisted TSC scaling but only for L1
> > > and it
> > > doesn't expose the feature to nested guests. This patch series adds
> > > support for
> > > nested TSC scaling and allows both L1 and L2 to be scaled with
> > > different
> > > scaling factors.
> > > 
> > > When scaling and offsetting is applied, the TSC for the guest is
> > > calculated as:
> > > 
> > > (TSC * multiplier >> 48) + offset
> > > 
> > > With nested scaling the values in VMCS01 and VMCS12 need to be
> > > merged
> > > together and stored in VMCS02.
> > > 
> > > The VMCS02 values are calculated as follows:
> > > 
> > > offset_02 = ((offset_01 * mult_12) >> 48) + offset_12
> > > mult_02 = (mult_01 * mult_12) >> 48
> > > 
> > > The last patch of the series adds a KVM selftest.
> > 
> > Will you be doing the same for SVM? The last time I tried to add a
> > nested virtualization feature for Intel only, Paolo rapped my knuckles
> > with a ruler.
> 
> Yes, I can try do this, if it's not much more complicated, once I get
> access to AMD hardware. 

I have access to AMD hardware with regular TSC scaling,
and nested TSC scaling IMHO won't be hard for me to implement 
so I volunteer for this task! 


Best regards,
	Maxim Levitsky

> 
> But I suppose this series is standalone and could be merged separately?
> By taking a quick look it seems that SVM exposes far less features to
> nested guests than VMX does anyway.
> 
> Ilias