linux-kernel - Re: [PATCH v2] KVM: const-ify all relevant uses of struct kvm_memory

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Date:   Mon, 2 Aug 2021 15:40:08 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Hamza Mahfooz <someguy@...ective-light.com>,
        linux-kernel@...r.kernel.org
Cc:     Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        kvm@...r.kernel.org
Subject: Re: [PATCH v2] KVM: const-ify all relevant uses of struct
 kvm_memory_slot

On 31/07/21 00:27, Hamza Mahfooz wrote:
> @@ -1440,7 +1440,7 @@ static bool kvm_set_pte_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
>   
>   struct slot_rmap_walk_iterator {
>   	/* input fields. */
> -	struct kvm_memory_slot *slot;
> +	const struct kvm_memory_slot *slot;
>   	gfn_t start_gfn;
>   	gfn_t end_gfn;
>   	int start_level;
> @@ -1467,16 +1467,20 @@ rmap_walk_init_level(struct slot_rmap_walk_iterator *iterator, int level)
>   
>   static void
>   slot_rmap_walk_init(struct slot_rmap_walk_iterator *iterator,
> -		    struct kvm_memory_slot *slot, int start_level,
> +		    const struct kvm_memory_slot *slot, int start_level,
>   		    int end_level, gfn_t start_gfn, gfn_t end_gfn)
>   {
> -	iterator->slot = slot;
> -	iterator->start_level = start_level;
> -	iterator->end_level = end_level;
> -	iterator->start_gfn = start_gfn;
> -	iterator->end_gfn = end_gfn;
> +	struct slot_rmap_walk_iterator iter = {
> +		.slot = slot,
> +		.start_gfn = start_gfn,
> +		.end_gfn = end_gfn,
> +		.start_level = start_level,
> +		.end_level = end_level
> +	};
> +
> +	rmap_walk_init_level(&iter, start_level);
>   
> -	rmap_walk_init_level(iterator, iterator->start_level);
> +	memcpy(iterator, &iter, sizeof(struct slot_rmap_walk_iterator));
>   }
>   
>   static bool slot_rmap_walk_okay(struct slot_rmap_walk_iterator *iterator)

I don't understand, just changing the argument works.  There is no need 
to change the body of the function.

Paolo