Re: KVM swapping with mmu notifiers

[Andrea Arcangeli <andrea-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

On Tue, Jan 22, 2008 at 03:37:59PM +0200, Avi Kivity wrote:
> Andrea Arcangeli wrote:
>> On Sun, Jan 20, 2008 at 05:16:03PM +0200, Avi Kivity wrote:
>>   
>>> Yes, it's supposed to work (we can't prevent userspace from doing it).
>>>     
>>
>> Hmm, I think we already prevent it, so I don't think I need to update
>> my swap code until the below is removed.
>>
>> 	/* Check for overlaps */
>> 	r = -EEXIST;
>> 	for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
>> 		struct kvm_memory_slot *s = &kvm->memslots[i];
>>
>> 		if (s == memslot)
>> 			continue;
>> 		if (!((base_gfn + npages <= s->base_gfn) ||
>> 		      (base_gfn >= s->base_gfn + s->npages)))
>> 			goto out_free;
>> 	}
>>
>>   
>
> Actually, this checks against slots with the overlapping gfns.  Aliases 
> have different gfns but same hvas.

Hmm not sure to follow, do you mean I need to change something?
Aliases live in a different dimension, and I can't see how my code
could ever notice or care about aliases (that have to be translated to
a real hva-memslot-backed gfn before calling get_user_pages). All I
care about are to find the right rmap structures for each hva. The
above snippet should be enough to guarantee that there can only be 1
rmap structure for each hva, so when I checked yesterday that looked
enough to prove my kvm_hva_to_rmapp implementation already correct.

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