Re: [RFC PATCH v0 2/2] KVM: PPC: Book3S HV: Use H_RPT_INVALIDATE in nested KVM

On Thu, Jul 09, 2020 at 08:07:11PM +1000, Paul Mackerras wrote:

On Thu, Jul 09, 2020 at 02:38:51PM +0530, Bharata B Rao wrote:

quoted

On Thu, Jul 09, 2020 at 03:18:03PM +1000, Paul Mackerras wrote:

quoted

On Fri, Jul 03, 2020 at 04:14:20PM +0530, Bharata B Rao wrote:

quoted

In the nested KVM case, replace H_TLB_INVALIDATE by the new hcall
H_RPT_INVALIDATE if available. The availability of this hcall
is determined from "hcall-rpt-invalidate" string in ibm,hypertas-functions
DT property.

What are we going to use when nested KVM supports HPT guests at L2?
L1 will need to do partition-scoped tlbies with R=0 via a hypercall,
but H_RPT_INVALIDATE says in its name that it only handles radix
page tables (i.e. R=1).

For L2 HPT guests, the old hcall is expected to work after it adds
support for R=0 case?

That was the plan.

quoted

The new hcall should be advertised via ibm,hypertas-functions only
for radix guests I suppose.

Well, the L1 hypervisor is a radix guest of L0, so it would have
H_RPT_INVALIDATE available to it?

I guess the question is whether H_RPT_INVALIDATE is supposed to do
everything, that is, radix process-scoped invalidations, radix
partition-scoped invalidations, and HPT partition-scoped
invalidations.  If that is the plan then we should call it something
different.

Guess we are bit late now to rename it and include HPT in the scope.

This patchset seems to imply that H_RPT_INVALIDATE is at least going
to be used for radix partition-scoped invalidations as well as radix
process-scoped invalidations.  If you are thinking that in future when
we need HPT partition-scoped invalidations for a radix L1 hypervisor
running a HPT L2 guest, we are going to define a new hypercall for
that, I suppose that is OK, though it doesn't really seem necessary.

Guess a new hcall would be the way forward to cover the HPT L2 guest
requirements.

Thanks for pointing this out.

Regards,
Bharata.