linux-kernel - Re: [PATCH v4 3/7] KVM: Add lockless memslot walk to KVM

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Date: Wed, 29 May 2024 20:26:41 -0700
From: James Houghton <jthoughton@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Paolo Bonzini <pbonzini@...hat.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Ankit Agrawal <ankita@...dia.com>, 
	Anup Patel <anup@...infault.org>, Atish Patra <atishp@...shpatra.org>, 
	Axel Rasmussen <axelrasmussen@...gle.com>, Bibo Mao <maobibo@...ngson.cn>, 
	Catalin Marinas <catalin.marinas@....com>, David Matlack <dmatlack@...gle.com>, 
	David Rientjes <rientjes@...gle.com>, Huacai Chen <chenhuacai@...nel.org>, 
	James Morse <james.morse@....com>, Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>, 
	Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, 
	Oliver Upton <oliver.upton@...ux.dev>, Palmer Dabbelt <palmer@...belt.com>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Raghavendra Rao Ananta <rananta@...gle.com>, 
	Ryan Roberts <ryan.roberts@....com>, Shaoqin Huang <shahuang@...hat.com>, 
	Shuah Khan <shuah@...nel.org>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>, 
	Zenghui Yu <yuzenghui@...wei.com>, kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org, 
	kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-mips@...r.kernel.org, 
	linux-mm@...ck.org, linux-riscv@...ts.infradead.org, 
	linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev
Subject: Re: [PATCH v4 3/7] KVM: Add lockless memslot walk to KVM

On Wed, May 29, 2024 at 2:51 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Wed, May 29, 2024, James Houghton wrote:
> > @@ -686,10 +694,12 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
> >       return __kvm_handle_hva_range(kvm, &range).ret;
> >  }
> >
> > -static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn,
> > -                                                      unsigned long start,
> > -                                                      unsigned long end,
> > -                                                      gfn_handler_t handler)
> > +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 = mmu_notifier_to_kvm(mn);
> >       const struct kvm_mmu_notifier_range range = {
> > @@ -699,6 +709,7 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn
> >               .on_lock        = (void *)kvm_null_fn,
> >               .flush_on_ret   = false,
> >               .may_block      = false,
> > +             .lockless       = lockless,
>
> Why add @lockess to kvm_handle_hva_range_no_flush()?  Both callers immediately
> 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_notifier *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
> >