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

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On Tue, Jan 24, 2023 at 8:32 AM Ricardo Koller <ricarkol@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx> 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?

I like this, but please don't use elide in the code. I'm all for
vocabulary, but that's not a common enough word to expect everyone to
know. Perhaps just SKIP?

>
> > 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



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