Re: [Xen-devel] [PATCH v2] x86/mm: Add mem access rights to NPT

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx> 06/28/18 4:58 PM >>>
>On 06/28/2018 05:53 PM, Alexandru Stefan ISAILA wrote:
>> The number was with this patch so no correction. This was done with
>> xen-access write and I don't think it will make a difference if you
>> change the access to all the mem pages.
>
>Right, so the average is the average between runs of "xen-access <DOMID>
>write", which sets all of the domain's pages to r-x. A typical
>introspection application will not set all of the domain's pages up this
>way - so the number is an average of maximums.
>
>AFAIK ARM uses this model - are there fewer pages in a typical ARM
>guest, or are we missing something about the way they are using radix
>trees for this purpose? Or perhaps the ARM code should be changed as well?

Whether the over head with introspection in use is tolerable is something
you guys need to know. As said in the other reply - my worries are about
extra overhead without introspection in use. If the radix tree was never used
in such a case, it would be more clearly visible that there is no overhead if
the creation of the radix tree at domain creation time was avoided.


Jan


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