Re: [Xen-devel] [PATCH v1 2/2] ioreq-server: Support scatter page forwarding

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.08.14 at 23:39, <kevin.tian@xxxxxxxxx> wrote:
>>  From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> So am I reading this right that you could do with the existing
>> mechanism if the limit was higher? Together with you not answering
>> the question about the lack of an enforced limit in your new
>> mechanism, this clearly tells me that you should use the existing one,
>> raising the limit and - if necessary - dealing with the (security) fallout.
>> 
> 
> essentially those pages are not contiguous and dynamic, and thus a fixed 
> range based structure even with a higher limitation doesn't fit here. Just
> think about a structure similar to what we have done to maintain shadow
> pfn is required here. A hash list is more flexible to serve such purpose.

I don't follow - range sets aren't a "fixed range based structure" to
me. All we impose is a limit on the number of ranges you may have
in place to avoid unbounded amounts of memory being tied up by a
domain, or unbounded amounts of time are spent in accessing that
tree. Obviously the same would need to be done for any new
mechanism, so a new mechanism is only first choice if it provides
other benefits over the original one.

Jan


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