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

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
> 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.

I think it may not be resubmited. Backend may have no idea at all if the guest 
is resume quickly, I remember. Or maybe I miss understand the interface between 
backend/frontend..

Thanks
Yunhong Jiang

> 
> -- Keir
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