Re: [PATCH 3/3] X86: Add a thread cpu time implementation to vDSO

From: Chris Mason
Date: Mon Dec 15 2014 - 13:37:16 EST

On Thu, Dec 11, 2014 at 1:36 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:

* Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:

On Wed, Dec 10, 2014 at 2:56 PM, Shaohua Li <shli@xxxxxx> wrote:
> On Wed, Dec 10, 2014 at 02:13:23PM -0800, Andy Lutomirski wrote:
>> On Wed, Dec 10, 2014 at 1:57 PM, Shaohua Li <shli@xxxxxx> wrote:
>> > On Wed, Dec 10, 2014 at 11:10:52AM -0800, Andy Lutomirski wrote:
>> >> On Sun, Dec 7, 2014 at 7:03 PM, Shaohua Li <shli@xxxxxx> wrote:
>> >> > This primarily speeds up clock_gettime(CLOCK_THREAD_CPUTIME_ID, ..). We
>> >> > use the following method to compute the thread cpu time:
>> >>
>> >> I like the idea, and I like making this type of profiling fast. I
>> >> don't love the implementation because it's an information leak (maybe
>> >> we don't care) and it's ugly.
>> >>
>> >> The info leak could be fixed completely by having a per-process array
>> >> instead of a global array. That's currently tricky without wasting
>> >> memory, but it could be created on demand if we wanted to do that,
>> >> once my vvar .fault patches go in (assuming they do -- I need to ping
>> >> the linux-mm people).
>> >
>> > those info leak really doesn't matter.
>> Why not?
> Ofcourse I can't make sure completely, but how could this
> info be used as attack?

It may leak interesting timing info, even from cpus that are
outside your affinity mask / cpuset. I don't know how much
anyone actually cares.

Finegraned timing information has been successfully used to
recover secret keys (and sometimes even coarse timing
information), so it can be a security issue in certain setups.

Trying to nail this down a little more clearly. Are you worried about the context switch count being exported or the clock_gettime data?


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at