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

["Stamatis, Ilias" <ilstam@amazon.com>]

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. 

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