Re: [PATCH 1/9] KVM: arm64: Add KVM_PGTABLE_WALK_REMOVED into ctx->flags

[Ricardo Koller <ricarkol@google.com>]

On Tue, Jan 24, 2023 at 12:56:11AM +0000, Oliver Upton wrote:
> On Mon, Jan 23, 2023 at 04:51:16PM -0800, Ben Gardon wrote:
> > On Thu, Jan 12, 2023 at 7:50 PM Ricardo Koller <ricarkol@google.com> wrote:
> > >
> > > Add a flag to kvm_pgtable_visit_ctx, KVM_PGTABLE_WALK_REMOVED, to
> > > indicate that the walk is on a removed table not accesible to the HW
> > > page-table walker. Then use it to avoid doing break-before-make or
> > > performing CMOs (Cache Maintenance Operations) when mapping a removed
> > 
> > Nit: Should this say unmapping? Or are we actually going to use this
> > to map memory ?
> 
> I think the *_REMOVED term feels weird as it relates to constructing a
> page table. It'd be better if we instead added flags to describe the
> operations we intend to elide (i.e. CMOs and TLBIs).

What about KVM_PGTABLE_WALK_ELIDE_BBM and KVM_PGTABLE_WALK_ELIDE_CMO?

> That way the
> implementation is generic enough that we can repurpose it for other use
> cases.

Aha, good point. I actually have a use case for it (FEAT_BBM).

> 
> --
> Thanks,
> Oliver