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

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

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.

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.

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.

Paul.