From: Ricardo Koller <ricarkol@google.com>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: pbonzini@redhat.com, maz@kernel.org, dmatlack@google.com,
qperret@google.com, catalin.marinas@arm.com,
andrew.jones@linux.dev, seanjc@google.com,
alexandru.elisei@arm.com, suzuki.poulose@arm.com,
eric.auger@redhat.com, gshan@redhat.com, reijiw@google.com,
rananta@google.com, bgardon@google.com, kvm@vger.kernel.org,
kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,
ricarkol@gmail.com
Subject: Re: [RFC PATCH 02/12] KVM: arm64: Allow visiting block PTEs in post-order
Date: Thu, 12 Jan 2023 19:44:43 -0800 [thread overview]
Message-ID: <Y8DTqxdY/h4f0q4a@google.com> (raw)
In-Reply-To: <Y3KNZCLVqnFeg7hi@google.com>
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@google.com>
> > ---
> > 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
next prev parent reply other threads:[~2023-01-13 3:44 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-12 8:17 [RFC PATCH 00/12] KVM: arm64: Eager huge-page splitting for dirty-logging Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 01/12] KVM: arm64: Relax WARN check in stage2_make_pte() Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-14 20:59 ` Oliver Upton
2022-11-14 20:59 ` Oliver Upton
2022-11-12 8:17 ` [RFC PATCH 02/12] KVM: arm64: Allow visiting block PTEs in post-order Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-14 18:48 ` Oliver Upton
2022-11-14 18:48 ` Oliver Upton
2023-01-13 3:44 ` Ricardo Koller [this message]
2022-11-12 8:17 ` [RFC PATCH 03/12] KVM: arm64: Add stage2_create_removed() Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 04/12] KVM: arm64: Add kvm_pgtable_stage2_split() Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-14 20:54 ` Oliver Upton
2022-11-14 20:54 ` Oliver Upton
2022-11-15 23:03 ` Ricardo Koller
2022-11-15 23:03 ` Ricardo Koller
2022-11-15 23:27 ` Ricardo Koller
2022-11-15 23:27 ` Ricardo Koller
2022-11-15 23:54 ` Oliver Upton
2022-11-15 23:54 ` Oliver Upton
2022-11-17 21:50 ` Ricardo Koller
2022-11-17 21:50 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 05/12] arm64: Add a capability for FEAT_BBM level 2 Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 06/12] KVM: arm64: Split block PTEs without using break-before-make Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-14 18:56 ` Oliver Upton
2022-11-14 18:56 ` Oliver Upton
2022-11-12 8:17 ` [RFC PATCH 07/12] KVM: arm64: Refactor kvm_arch_commit_memory_region() Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 08/12] KVM: arm64: Add kvm_uninit_stage2_mmu() Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 09/12] KVM: arm64: Split huge pages when dirty logging is enabled Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 10/12] KVM: arm64: Open-code kvm_mmu_write_protect_pt_masked() Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 11/12] KVM: arm64: Split huge pages during KVM_CLEAR_DIRTY_LOG Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-12 8:17 ` [RFC PATCH 12/12] KVM: arm64: Use local TLBI on permission relaxation Ricardo Koller
2022-11-12 8:17 ` Ricardo Koller
2022-11-14 18:42 ` [RFC PATCH 00/12] KVM: arm64: Eager huge-page splitting for dirty-logging Oliver Upton
2022-11-14 18:42 ` Oliver Upton
2023-01-13 3:42 ` Ricardo Koller
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