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Re: [Xen-devel] [PATCH for-4.5 v11 0/9] Mem_event and mem_access for ARM

On Mon, Sep 29, 2014 at 1:36 PM, Tamas K Lengyel <tklengyel@xxxxxxxxxxxxx> wrote:

The ARM virtualization extension provides 2-stage paging, a similar mechanisms
to Intel's EPT, which can be used to trace the memory accesses performed by
the guest systems. This series sets up the necessary infrastructure in the ARM code
to deliver the event on R/W/X traps. Finally, we turn on the compilation of
mem_access and mem_event on ARM and perform the necessary changes to the tools side.

While the series is marked for-4.5, I certainly don't mind having these remaining parts delayed till 4.6 as nothing depends on this feature being in 4.5. It would make some security researchers life a lot easier if they could install a stable Xen release with this feature already in-place. Beyond that I don't think there is an audience for it (yet). IMHO I think its close to be done but if the general feel is that it wasn't reviewed enough and there is some hesitance, I'm OK with a couple more rounds of reviews.

It has also been proposed that a proper analysis for overhead be performed on this series as to show it does not add too much overhead to non-mem_access users. What that entails is unclear to me and IMHO it's not an easy task considering all the corner-cases and use-cases that would need to be covered to be comprehensive. It has been my goal during this series to minimize the overhead added and to be on-par with the x86 side, but I'm afraid a more in-depth analysis is not something I can contribute. Of course, if specific instances of overhead added are pointed out in the code that can be avoided, I'm happy to do so.

Thanks,
Tamas

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