linux-kernel - Re: [PATCH 10/14] KVM: x86: Further clarify the logic and comments for toggling log dirty

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Date:   Thu, 18 Feb 2021 13:50:51 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        Makarand Sonare <makarandsonare@...gle.com>
Subject: Re: [PATCH 10/14] KVM: x86: Further clarify the logic and comments
 for toggling log dirty

On 13/02/21 01:50, Sean Christopherson wrote:
> 
> -	 * Nothing to do for RO slots or CREATE/MOVE/DELETE of a slot.
> -	 * See comments below.
> +	 * Nothing to do for RO slots (which can't be dirtied and can't be made
> +	 * writable) or CREATE/MOVE/DELETE of a slot.  See comments below.
>  	 */
>  	if ((change != KVM_MR_FLAGS_ONLY) || (new->flags & KVM_MEM_READONLY))
>  		return;
>  
> +	/*
> +	 * READONLY and non-flags changes were filtered out above, and the only
> +	 * other flag is LOG_DIRTY_PAGES, i.e. something is wrong if dirty
> +	 * logging isn't being toggled on or off.
> +	 */
> +	if (WARN_ON_ONCE(!((old->flags ^ new->flags) & KVM_MEM_LOG_DIRTY_PAGES)))
> +		return;
> +

What about readonly -> readwrite changes?

Paolo