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

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Message-ID: <ZlejXCYIuJ7_DlwL@google.com>
Date: Wed, 29 May 2024 14:51:24 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: James Houghton <jthoughton@...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, 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.

>  {
>  	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.

>  	};
>  
>  	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
>