Re: [RFC PATCH 0/2] Alloc kfence_pool after system startup

[Alexander Potapenko <glider@google.com>]

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On Thu, Mar 3, 2022 at 4:15 AM Tianchen Ding <dtcccc@linux.alibaba.com>
wrote:

> KFENCE aims at production environments, but it does not allow enabling
> after system startup because kfence_pool only alloc pages from memblock.
> Consider the following production scene:
> At first, for performance considerations, production machines do not
> enable KFENCE.
>
What are the performance considerations you have in mind? Are you running
KFENCE with a very aggressive sampling rate?

However, after running for a while, the kernel is suspected to have
> memory errors. (e.g., a sibling machine crashed.)
>
I have doubts regarding this setup. It might be faster (although one can
tune KFENCE to have nearly zero performance impact), but is harder to
maintain.
It will also catch fewer errors than if you just had KFENCE on from the
very beginning:
 - sibling machines may behave differently, and a certain bug may only
occur once - in that case the secondary instances won't notice it, even
with KFENCE;
 - KFENCE also catches non-lethal corruptions (e.g. OOB reads), which may
stay under radar for a very long time.


> So other production machines need to enable KFENCE, but it's hard for
> them to reboot.
>
> The 1st patch allows re-enabling KFENCE if the pool is already
> allocated from memblock.
>
> The 2nd patch applies the main part.
>
> Tianchen Ding (2):
>   kfence: Allow re-enabling KFENCE after system startup
>   kfence: Alloc kfence_pool after system startup
>
>  mm/kfence/core.c | 106 ++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 87 insertions(+), 19 deletions(-)
>
> --
> 2.27.0
>
>

-- 
Alexander Potapenko
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