Re: [PATCH] kvm: fix to update memslots properly

[Paolo Bonzini <pbonzini@redhat.com>]

>>> This suggests another fix.  We can change the insertion to use a ">="
>>> comparison, as in your first patch.  Alone it is not correct, but we
>>> only need to take some care and avoid breaking the case of deleting a
>>> memslot.
>>>
>>> It's enough to wrap the second loop (that you patched) with
>>> "if (new->npages)".  In the new->npages == 0 case the first loop has
>>> already set i to the right value, and moving i back would be wrong:
>>>
>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>>> index f5283438ee05..050974c051b5 100644
>>> --- a/virt/kvm/kvm_main.c
>>> +++ b/virt/kvm/kvm_main.c
>>> @@ -687,11 +687,23 @@ static void update_memslots(struct kvm_memslots
>>> *slots,
>>>           slots->id_to_index[mslots[i].id] = i;
>>>           i++;
>>>       }
>>> -    while (i > 0 &&
>>> -           new->base_gfn > mslots[i - 1].base_gfn) {
>>> -        mslots[i] = mslots[i - 1];
>>> -        slots->id_to_index[mslots[i].id] = i;
>>> -        i--;
>>> +
>>> +    /*
>>> +     * The ">=" is needed when creating a slot with base_gfn == 0,
>>> +     * so that it moves before all those with base_gfn == npages == 0.
>>> +     *
>>> +     * On the other hand, if new->npages is zero, the above loop has
>>> +     * already left i pointing to the beginning of the empty part of
>>> +     * mslots, and the ">=" would move the hole backwards in this
>>> +     * case---which is wrong.  So skip the loop when deleting a slot.
>>> +     */
>>> +    if (new->npages) {
>>> +        while (i > 0 &&
>>> +               new->base_gfn >= mslots[i - 1].base_gfn) {
>>> +            mslots[i] = mslots[i - 1];
>>> +            slots->id_to_index[mslots[i].id] = i;
>>> +            i--;
>>> +        }
>>>       }
>>>
>>>       mslots[i] = *new;
>>>
>>> Paolo
>>
>> Paolo,
>>
>> Can you include a proper changelog for this patch?
>>
> 
> But this is already applied long time ago...

Yes, this is commit efbeec7098eee2b3d2359d0cc24bbba0436e7f21.

Paolo