linux-kernel - Re: [PATCH v2 14/15] KVM: Terminate memslot walks via used

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Date:   Tue, 22 Oct 2019 08:28:27 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Hogan <jhogan@...nel.org>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 14/15] KVM: Terminate memslot walks via used_slots

On Tue, Oct 22, 2019 at 04:04:18PM +0200, Paolo Bonzini wrote:
> On 22/10/19 02:35, Sean Christopherson wrote:
> > +static inline int kvm_shift_memslots_forward(struct kvm_memslots *slots,
> > +					     struct kvm_memory_slot *new)
> > +{
> > +	struct kvm_memory_slot *mslots = slots->memslots;
> > +	int i;
> > +
> > +	if (WARN_ON_ONCE(slots->id_to_index[new->id] == -1) ||
> > +	    WARN_ON_ONCE(!slots->used_slots))
> > +		return -1;
> > +
> > +	for (i = slots->id_to_index[new->id]; i < slots->used_slots - 1; i++) {
> > +		if (new->base_gfn > mslots[i + 1].base_gfn)
> > +			break;
> > +
> > +		WARN_ON_ONCE(new->base_gfn == mslots[i + 1].base_gfn);
> > +
> > +		/* Shift the next memslot forward one and update its index. */
> > +		mslots[i] = mslots[i + 1];
> > +		slots->id_to_index[mslots[i].id] = i;
> > +	}
> > +	return i;
> > +}
> > +
> > +static inline int kvm_shift_memslots_back(struct kvm_memslots *slots,
> > +					  struct kvm_memory_slot *new,
> > +					  int start)
> 
> This new implementation of the insertion sort loses the comments that
> were there in the old one.  Please keep them as function comments.

I assume you're talking about this blurb in particular?

	 * The ">=" is needed when creating a slot with base_gfn == 0,
	 * so that it moves before all those with base_gfn == npages == 0.