On Mon, Nov 14, 2022 at 06:48:04PM +0000, Oliver Upton wrote:
> On Sat, Nov 12, 2022 at 08:17:04AM +0000, Ricardo Koller wrote:
> > The page table walker does not visit block PTEs in post-order. But there
> > are some cases where doing so would be beneficial, for example: breaking a
> > 1G block PTE into a full tree in post-order avoids visiting the new tree.
> >
> > Allow post order visits of block PTEs. This will be used in a subsequent
> > commit for eagerly breaking huge pages.
> >
> > Signed-off-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
> > ---
> > arch/arm64/include/asm/kvm_pgtable.h | 4 ++--
> > arch/arm64/kvm/hyp/nvhe/setup.c | 2 +-
> > arch/arm64/kvm/hyp/pgtable.c | 25 ++++++++++++-------------
> > 3 files changed, 15 insertions(+), 16 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
> > index e2edeed462e8..d2e4a5032146 100644
> > --- a/arch/arm64/include/asm/kvm_pgtable.h
> > +++ b/arch/arm64/include/asm/kvm_pgtable.h
> > @@ -255,7 +255,7 @@ struct kvm_pgtable {
> > * entries.
> > * @KVM_PGTABLE_WALK_TABLE_PRE: Visit table entries before their
> > * children.
> > - * @KVM_PGTABLE_WALK_TABLE_POST: Visit table entries after their
> > + * @KVM_PGTABLE_WALK_POST: Visit leaf or table entries after their
> > * children.
>
> It is not immediately obvious from this change alone that promoting the
> post-order traversal of every walker to cover leaf + table PTEs is safe.
>
> Have you considered using a flag for just leaf post-order visits?
>
Not using this commit in v1. There's no (noticeable) perf benefit from
avoiding visiting the new split tree.
Thanks,
Ricardo
> --
> Thanks,
> Oliver
