Subject: Re: [PATCH v4 3/7] KVM: Add lockless memslot walk to KVM

From: Sean Christopherson <[email-masked]>
Date: Wed, 29 May 2024 14:51:24 -0700

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
>