[seL4] Change Access Right to Memory Pages

Norrathep Rattanavipanon nrattana at uci.edu
Tue May 2 16:07:14 AEST 2017


Yes, you are absolutely right about that. I think it would be good to
include the map time (even though called it once) for completeness :).

On Mon, May 1, 2017 at 10:36 PM, <Gernot.Heiser at data61.csiro.au> wrote:

> Hi Oak,
>
> My understanding is that in your use case, the map is a one-off and
> therefore not performance-critical, while the re-map needs to be done on
> each snapshot and therefore is performance-critical.
>
> I hope the student gets to evaluate alternative implementation so we can
> see how much benefit bulk operations would provide.
>
> Gernot
>
> On 2 May 2017, at 15:32 , Norrathep Rattanavipanon <nrattana at uci.edu>
> wrote:
>
> Hi Adrain and Gernot,
>
> Thank you for the clarification. Yes, sorry, forgot to mention that we are
> using ARM i.MX6 Sabre Lite and forgot to mention some backgrounds.
>
> We are interested in benchmarking (1) the time to lock large memory
> regions (switching from R/W to R/O) and (2) the time to map large memory
> regions as Gernot mentioned its for providing a consistent snapshot of user
> memory.
> So just to make sure the current implementation for that is the optimal
> remap (modify paging structure, clean cache, invalidate tlb), correct?
>
> @Gernot, right, per our discussion, we only discussed out a bulk mapping
> operation (mapping from other processes into the root process) but I was
> not sure about locking (which is remapping in this case). Thank you for
> confirming.
>
> Best,
> Oak
>
> On Mon, May 1, 2017 at 10:18 PM, <Gernot.Heiser at data61.csiro.au> wrote:
>
>> On 2 May 2017, at 3:21 , Norrathep Rattanavipanon <nrattana at uci.edu>
>> wrote:
>>
>>
>> 2) If my understanding in 1) is correct, the remap function only takes 1
>> cap at a time.
>> So if I want to modify access rights of many pages, do I have to call the
>> remap function multiple times?
>> Or is there a more efficient way to do so?
>>
>>
>> Hi Oak,
>>
>> As we discussed in person, this is a known issue of our API, and I have
>> presently a student doing some evaluations. I have your use case in mind
>> when talking to the student – for everyone else’s benefit, this is about a
>> consistent shapshot of user memory for doing remote attestation.
>>
>> I would be interested in other use cases for a bulk re-mapping operation.
>> I suspect that there are use cases where this might be a bottleneck, but it
>> would be good to identify specific cases of enough significance to consider
>> an API change. Certainly there won’t be a change if we don’t have
>> convincing use cases.
>>
>> Gernot
>>
>
>
>
> --
> Norrathep (Oak) Rattanavipanon
> M.S. in Computer Science
> University of California - Irvine
>
>
>


-- 
Norrathep (Oak) Rattanavipanon
M.S. in Computer Science
University of California - Irvine
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