Re: [Xen-devel] Re: [PATCH] Support swap a page from user spacetools -- Was RE: [RFC][PATCH] Basic support for page offline

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 20/03/2009 09:37, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>> 5) After update all page tables, user space tools will try to exchange the
>> old page with the new page. If the new mfn has no
>> reference anymore (i.e. count_info & count_mask = 1), the exchange will
>> update the m2p and return success, otherwise it will
>> return fail. (the page may be referenced by other domain, like grant table or
>> foreign mapped).
> 
> Hmm, if you consider the possibility of this case, then you should also
> consider the possibility of a page still being accessible by another domain at
> the point where you copy its content, but no longer in use when you do the
> exchange (which means that the content may have changed between the two points
> in time).

Since the guest is suspended, would that matter? Any I/Os that were in
flight on suspend will get resubmitted on resume. So the potential races
might all be benign.

 -- Keir



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