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

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Message-Id: <XFS2XQ.ZZ0IWDD0G95J@effective-light.com>
Date:   Fri, 30 Jul 2021 16:47:57 -0400
From:   Hamza Mahfooz <someguy@...ective-light.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...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] KVM: const-ify all relevant uses of struct
 kvm_memory_slot


Hey Peter,

On Fri, Jul 30 2021 at 04:19:21 PM -0400, Peter Xu <peterx@...hat.com> 
wrote:
> This patch breaks kvm/queue with above issue.  Constify of 
> kvm_memory_slot
> pointer should have nothing to do with this so at least it should 
> need a
> separate patch.  At the meantime I also don't understand why memcpy() 
> here,
> which seems to be even slower..

To const-ify the slot member of struct slot_rmap_walk_iterator, we need 
to
initialize a new struct and then copy it over (otherwise we would need 
to relay
on casting again or the compiler will complain about it).