From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sean Christopherson <seanjc@google.com>
Date: Fri, 12 Nov 2021 01:05:27 +0000
Subject: Re: [PATCH v5.5 24/30] KVM: Use interval tree to do fast hva lookup in memslots
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 <20211104002531.1176691-25-seanjc@google.com>
 <d76707b5-8710-b1a6-0cc6-defdaf9e37b7@oracle.com>
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To: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
Cc: James Morse <james.morse@arm.com>, Alexandru Elisei <alexandru.elisei@arm.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Atish Patra <atish.patra@wdc.com>, David Hildenbrand <david@redhat.com>, Cornelia Huck <cohuck@redhat.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, Vitaly Kuznetsov <vkuznets@redhat.com>, Wanpeng Li <wanpengli@tencent.com>, Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Ben Gardon <bgardon@google.com>, Marc Zyngier <maz@kernel.org>, Huacai Chen <chenhuacai@kernel.org>, Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>, Paul Mackerras <paulus@ozlabs.org>, Anup Patel <anup.patel@wdc.com>, Paul Walmsley <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, Christian Borntraeger <borntraeger@de.ibm.com>, Janosch Frank <frankja@linux.ibm.com>, Paolo Bonzini <pbonzini@redhat.com>

On Fri, Nov 12, 2021, Maciej S. Szmigiero wrote:
> On 04.11.2021 01:25, Sean Christopherson wrote:
> > @@ -1262,22 +1274,32 @@ static void kvm_replace_memslot(struct kvm_memslots *slots,
> >   				struct kvm_memory_slot *new)
> >   {
> >   	/*
> > -	 * Remove the old memslot from the hash list, copying the node data
> > -	 * would corrupt the list.
> > +	 * Remove the old memslot from the hash list and interval tree, copying
> > +	 * the node data would corrupt the structures.
> >   	 */
> >   	if (old) {
> >   		hash_del(&old->id_node);
> > +		interval_tree_remove(&old->hva_node, &slots->hva_tree);
> >   		if (!new)
> >   			return;
> >   	}
> > -	/* Copy the source *data*, not the pointer, to the destination. */
> > -	if (old)
> > +	/*
> > +	 * Copy the source *data*, not the pointer, to the destination.  If
> > +	 * @old is NULL, initialize @new's hva range.
> > +	 */
> > +	if (old) {
> >   		*new = *old;
> > +	} else if (new) {
> 
> Unnecessary check - if "new" is NULL then the code will crash anyway
> accessing this pointer unconditionally...
> 
> > +		new->hva_node.start = new->userspace_addr;
> > +		new->hva_node.last = new->userspace_addr +
> > +				     (new->npages << PAGE_SHIFT) - 1;
> > +	}
> >   	/* (Re)Add the new memslot. */
> >   	hash_add(slots->id_hash, &new->id_node, new->id);
> > +	interval_tree_insert(&new->hva_node, &slots->hva_tree);
> 
> ...in these two lines above.

Yep, definitely worthless.  I think this was another "plan for the future" idea
that didn't actually add value.