linux-kernel - Re: [PATCH 14/22] KVM: x86/mmu: Morph kvm_handle_gfn

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Message-ID: <CALzav=cYv4ZqD5q6-hP=WN8gYFxt7xYKCTm8dLaGtjk-kmCy=w@mail.gmail.com>
Date: Mon, 12 Aug 2024 14:53:29 -0700
From: David Matlack <dmatlack@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Oliver Upton <oliver.upton@...ux.dev>, Marc Zyngier <maz@...nel.org>, Peter Xu <peterx@...hat.com>, 
	James Houghton <jthoughton@...gle.com>
Subject: Re: [PATCH 14/22] KVM: x86/mmu: Morph kvm_handle_gfn_range() into an
 aging specific helper

On Fri, Aug 9, 2024 at 12:48 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 0a33857d668a..88b656a1453d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> +static bool kvm_rmap_age_gfn_range(struct kvm *kvm,
> +                                  struct kvm_gfn_range *range, bool test_only)
> +{
> +       struct slot_rmap_walk_iterator iterator;
> +       struct rmap_iterator iter;
> +       bool young = false;
> +       u64 *sptep;
> +
> +       for_each_slot_rmap_range(range->slot, PG_LEVEL_4K, KVM_MAX_HUGEPAGE_LEVEL,
> +                                range->start, range->end - 1, &iterator) {
> +               for_each_rmap_spte(iterator.rmap, &iter, sptep) {
> +                       if (test_only && is_accessed_spte(*sptep))
> +                               return true;
> +
> +                       young = mmu_spte_age(sptep);

It's jarring to see that mmu_spte_age() can get called in the
test_only case, even though I think the code is technically correct
(it will only be called if !is_accessed_spte() in which case
mmu_spte_age() will do nothing).