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 <20240529180510.2295118-5-jthoughton@google.com> <ZlekYljG7KJwblUj@google.com>
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From: James Houghton <jthoughton@google.com>
Date: Wed, 29 May 2024 20:27:45 -0700
Message-ID: <CADrL8HVZxoO33F2UJBoTjF_SXpxyZmH=RTM5G3stgo_kRPjazA@mail.gmail.com>
Subject: Re: [PATCH v4 4/7] KVM: Move MMU lock acquisition for
 test/clear_young to architecture
To: Sean Christopherson <seanjc@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Paolo Bonzini <pbonzini@redhat.com>, 
	Albert Ou <aou@eecs.berkeley.edu>, Ankit Agrawal <ankita@nvidia.com>, 
	Anup Patel <anup@brainfault.org>, Atish Patra <atishp@atishpatra.org>, 
	Axel Rasmussen <axelrasmussen@google.com>, Bibo Mao <maobibo@loongson.cn>, 
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	Tianrui Zhao <zhaotianrui@loongson.cn>, Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>, 
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On Wed, May 29, 2024 at 2:55=E2=80=AFPM Sean Christopherson <seanjc@google.=
com> wrote:
>
> On Wed, May 29, 2024, James Houghton wrote:
> > For implementation mmu_notifier_{test,clear}_young, the KVM memslot
> > walker used to take the MMU lock for us. Now make the architectures
> > take it themselves.
>
> Hmm, *forcing* architectures to take mmu_lock is a step backwards.  Rathe=
r than
> add all of this churn, what about adding CONFIG_KVM_MMU_NOTIFIER_LOCKLESS=
, e.g.
>
> static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notif=
ier *mn,
>                                                          unsigned long st=
art,
>                                                          unsigned long en=
d,
>                                                          gfn_handler_t ha=
ndler)
> {
>         struct kvm *kvm =3D mmu_notifier_to_kvm(mn);
>         const struct kvm_mmu_notifier_range range =3D {
>                 .start          =3D start,
>                 .end            =3D end,
>                 .handler        =3D handler,
>                 .on_lock        =3D (void *)kvm_null_fn,
>                 .flush_on_ret   =3D false,
>                 .may_block      =3D false,
>                 .lockless       =3D IS_ENABLED(CONFIG_KVM_MMU_NOTIFIER_LO=
CKLESS),
>         };
>
>         return __kvm_handle_hva_range(kvm, &range).ret;
> }

Thanks Sean, yes this is a lot better. I will do this for v5.