Re: [PATCH v4 0/3] Fix bugs and performance of kstack offset randomisation

[Ryan Roberts <ryan.roberts@arm.com>]

On 19/01/2026 16:44, Kees Cook wrote:
> 
> 
> On January 19, 2026 8:00:00 AM PST, Dave Hansen <dave.hansen@intel.com> wrote:
>> On 1/19/26 05:01, Ryan Roberts wrote:
>>> x86 (AWS Sapphire Rapids):
>>> +-----------------+--------------+-------------+---------------+
>>> | Benchmark       | Result Class |   v6.18-rc5 | per-task-prng |
>>> |                 |              | rndstack-on |               |
>>> |                 |              |             |               |
>>> +=================+==============+=============+===============+
>>> | syscall/getpid  | mean (ns)    |  (R) 13.32% |     (R) 4.60% |
>>> |                 | p99 (ns)     |  (R) 13.38% |    (R) 18.08% |
>>> |                 | p99.9 (ns)   |      16.26% |    (R) 19.38% |
>>
>> Like you noted, this is surprising. This would be a good thing to make
>> sure it goes in very early after -rc1 and gets plenty of wide testing.
> 
> Right, we are pretty late in the dev cycle (rc6). It would be prudent to get this into -next after the coming rc1 (1 month from now).
> 
> On the other hand, the changes are pretty "binary" in the sense that mistakes should be VERY visible right away. Would it be better to take this into -next immediately instead?

I don't think this question was really addressed to me, but I'll give my opinion
anyway; I agree it's pretty binary - it will either work or it will explode.
I've tested on arm64 and x86_64 so I have high confidence that it works. If you
get it into -next ASAP it has 3 weeks to soak before the merge window opens
right? (Linus said he would do an -rc8 this cycle). That feels like enough time
to me. But it's your tree ;-)

Thanks,
Ryan


> 
>> But I don't see any problems with the approach, and the move to common
>> code looks like a big win as well:
> 
> Agreed; I think it's looking great.
>