Re: [PATCH v2 0/3] livepatch: Add "replace" sysfs attribute

[Petr Mladek <pmladek@suse.com>]

On Tue 2024-06-11 10:46:47, Yafang Shao wrote:
> On Tue, Jun 11, 2024 at 1:19 AM Song Liu <song@kernel.org> wrote:
> >
> > Hi Yafang,
> >
> > On Sun, Jun 9, 2024 at 6:33 PM Yafang Shao <laoar.shao@gmail.com> wrote:
> > >
> > > Add "replace" sysfs attribute to show whether a livepatch supports
> > > atomic replace or not.
> >
> > I am curious about the use case here.
> 
> We will use this flag to check if there're both atomic replace
> livepatch and non atomic replace livepatch running on a single server
> at the same time. That can happen if we install a new non atomic
> replace livepatch to a server which has already applied an atomic
> replace livepatch.
> 
> > AFAICT, the "replace" flag
> > matters _before_ the livepatch is loaded. Once the livepatch is
> > loaded, the "replace" part is already finished. Therefore, I think
> > we really need a way to check the replace flag before loading the
> > .ko file? Maybe in modinfo?
> 
> It will be better if we can check it before loading it. However it
> depends on how we build the livepatch ko, right? Take the
> kpatch-build[0] for example, we have to modify the kpatch-build to add
> support for it but we can't ensure all users will use it to build the
> livepatch.

> [0]. https://github.com/dynup/kpatch

I still do not understand how the sysfs attribute would help here.
It will show the type of the currently used livepatches. But
it won't say what the to-be-installed livepatch would do.

Could you please describe how exactly you would use the information?
What would be the process/algorithm/logic which would prevent a mistake?

Honestly, it sounds like your processes are broken and you try
to fix them on the wrong end.

Allowing to load random livepatches which are built a random way
sounds like a hazard.

It should be possible to load only livepatches which passed some
testing (QA). And the testing (QA) should check if the livepatch
successfully replaced the previous version.

Or do you want to use the sysfs attribute in QA?
So that only livepatches witch "replace" flag set would pass QA?

Best Regards,
Petr