[RFC PATCH untested] arm64: kernel: implement fast refcount checking

[Li Kun]

Hi Ard and Kees,

Yes, i have been working on this for several days, but i think Ard's 
patch is better than mine in some ways.
So i'll help reviewing the patch and try to give some suggestions.
Never mind:)

on 2017/7/26 1:20, Ard Biesheuvel wrote:
> On 25 July 2017 at 18:13, Kees Cook <keescook at chromium.org> wrote:
>> On Tue, Jul 25, 2017 at 4:49 AM, Ard Biesheuvel
>> <ard.biesheuvel at linaro.org> wrote:
>>> Hi all,
>>>
>>> I had a stab at porting the fast refcount checks to arm64. It is slightly
>>> less straight-forward than x86 given that we need to support both LSE and
>>> LL/SC, and fallback to the latter if running a kernel built with support
>>> for the former on hardware that does not support it.
>>>
>>> It is build tested with and without LSE support, and boots fine on non-LSE
>>> hardware in both cases.
>> Ah! Very cool. Hopefully you and Li can compare notes; I think they've
>> been working on an implementation too.
>>
> I wasn't aware of that.
>
>>> Suggestions welcome as to how to test and/or benchmark this,
>> I'll post a patch for LKDTM that I've been using. It's more
>> comprehensive than the existing ATOMIC checks (which predated the
>> refcount-only protection).
>>
> OK. One thing I couldn't figure out: is refcount_t signed or not? The
> saturate tests set the initial value to UINT_MAX - 1, but this is
> interpreted as a negative value and so the refcount manipulations that
> are expected to succeed also fail in my case.

-- 
Best Regards
Li Kun