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From: James Houghton <jthoughton@google.com>
Date: Wed, 29 May 2024 20:26:41 -0700
Message-ID: <CADrL8HUa9o+G6-Yn9oWt2LUgoVYGU=sYE2-JhkpoRgrS6Wi57g@mail.gmail.com>
Subject: Re: [PATCH v4 3/7] KVM: Add lockless memslot walk to KVM
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>, 
	Catalin Marinas <catalin.marinas@arm.com>, David Matlack <dmatlack@google.com>, 
	David Rientjes <rientjes@google.com>, Huacai Chen <chenhuacai@kernel.org>, 
	James Morse <james.morse@arm.com>, Jonathan Corbet <corbet@lwn.net>, Marc Zyngier <maz@kernel.org>, 
	Michael Ellerman <mpe@ellerman.id.au>, Nicholas Piggin <npiggin@gmail.com>, 
	Oliver Upton <oliver.upton@linux.dev>, Palmer Dabbelt <palmer@dabbelt.com>, 
	Paul Walmsley <paul.walmsley@sifive.com>, Raghavendra Rao Ananta <rananta@google.com>, 
	Ryan Roberts <ryan.roberts@arm.com>, Shaoqin Huang <shahuang@redhat.com>, 
	Shuah Khan <shuah@kernel.org>, Suzuki K Poulose <suzuki.poulose@arm.com>, 
	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 2:51=E2=80=AFPM Sean Christopherson <seanjc@google.=
com> wrote:
>
> On Wed, May 29, 2024, James Houghton wrote:
> > @@ -686,10 +694,12 @@ static __always_inline int kvm_handle_hva_range(s=
truct mmu_notifier *mn,
> >       return __kvm_handle_hva_range(kvm, &range).ret;
> >  }
> >
> > -static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_no=
tifier *mn,
> > -                                                      unsigned long st=
art,
> > -                                                      unsigned long en=
d,
> > -                                                      gfn_handler_t ha=
ndler)
> > +static __always_inline int kvm_handle_hva_range_no_flush(
> > +             struct mmu_notifier *mn,
> > +             unsigned long start,
> > +             unsigned long end,
> > +             gfn_handler_t handler,
> > +             bool lockless)
>
> Unnecessary and unwanted style change.

Sorry -- this will be fixed.

>
> >  {
> >       struct kvm *kvm =3D mmu_notifier_to_kvm(mn);
> >       const struct kvm_mmu_notifier_range range =3D {
> > @@ -699,6 +709,7 @@ static __always_inline int kvm_handle_hva_range_no_=
flush(struct mmu_notifier *mn
> >               .on_lock        =3D (void *)kvm_null_fn,
> >               .flush_on_ret   =3D false,
> >               .may_block      =3D false,
> > +             .lockless       =3D lockless,
>
> Why add @lockess to kvm_handle_hva_range_no_flush()?  Both callers immedi=
ately
> pass %false, and conceptually, locking is always optional for a "no flush=
" variant.

Right, this isn't needed in this patch. But I think I need it
eventually (like, in the next patch), so I'll move it where it is
really needed.


>
> >       };
> >
> >       return __kvm_handle_hva_range(kvm, &range).ret;
> > @@ -889,7 +900,8 @@ static int kvm_mmu_notifier_clear_young(struct mmu_=
notifier *mn,
> >        * cadence. If we find this inaccurate, we might come up with a
> >        * more sophisticated heuristic later.
> >        */
> > -     return kvm_handle_hva_range_no_flush(mn, start, end, kvm_age_gfn)=
;
> > +     return kvm_handle_hva_range_no_flush(mn, start, end,
> > +                                          kvm_age_gfn, false);
> >  }
> >
> >  static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
> > @@ -899,7 +911,7 @@ static int kvm_mmu_notifier_test_young(struct mmu_n=
otifier *mn,
> >       trace_kvm_test_age_hva(address);
> >
> >       return kvm_handle_hva_range_no_flush(mn, address, address + 1,
> > -                                          kvm_test_age_gfn);
> > +                                          kvm_test_age_gfn, false);
> >  }
> >
> >  static void kvm_mmu_notifier_release(struct mmu_notifier *mn,
> > --
> > 2.45.1.288.g0e0cd299f1-goog
> >