Re: Headers for whitelisted kernel functions available to BPF programs

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On Fri, Jun 4, 2021 at 12:11 PM Yonghong Song <yhs@xxxxxx> wrote:
> On 6/3/21 11:13 PM, Martin KaFai Lau wrote:
> >
> > Making the kfunc call whitelist more accessible is useful in general.
> > The bpf tcp-cc struct_ops is the only prog type supporting kfunc call.
> > What is your use case to introspect this whitelist?
>
> Agree. It would be good if you can share your use case.

At the high level, I am trying to see if we can use bpf in the drm
subsystem and gpu drivers which are kernel modules.  My initial
motivation was to use bpf for dynamic/run-time reconfiguration of the
drm/gpu driver (for experimentation.)  But now that I learned more
about bpf, I think there are quite a few more things I can do with it.
(Debugging during GPU hw bring-ups, profiling driver performance in
live system, etc.)  I have been looking into bpf with kprobe and
struct_ops.

In terms of kernel module support for bpf/btf, Andrii told me about it
last year and I see that his feature is in (I was able to do a btf
dump file for /sys/kernel/btf/amdgpu, /sys/kernel/btf/drm_ttm_helper,
for example.)  The next thing I thought about was having helper
functions from kernel modules and Toke pointed me to Martin's patch
around "unstable helpers"/calling whitelisted kernel functions and
this is where we are at.



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