Re: [PATCH bpf-next v2 2/3] bpf: export crash_kexec() as destructive kfunc

[Artem Savkov <asavkov@redhat.com>]

On Thu, Aug 04, 2022 at 01:41:53PM -0700, Alexei Starovoitov wrote:
> On Tue, Aug 2, 2022 at 2:10 AM Artem Savkov <asavkov@redhat.com> wrote:
> >
> > Allow properly marked bpf programs to call crash_kexec().
> >
> > Signed-off-by: Artem Savkov <asavkov@redhat.com>
> > ---
> >  kernel/kexec_core.c | 21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> >
> > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> > index 4d34c78334ce..9259ea3bd693 100644
> > --- a/kernel/kexec_core.c
> > +++ b/kernel/kexec_core.c
> > @@ -39,6 +39,8 @@
> >  #include <linux/hugetlb.h>
> >  #include <linux/objtool.h>
> >  #include <linux/kmsg_dump.h>
> > +#include <linux/btf.h>
> > +#include <linux/btf_ids.h>
> >
> >  #include <asm/page.h>
> >  #include <asm/sections.h>
> > @@ -1238,3 +1240,22 @@ void __weak arch_kexec_protect_crashkres(void)
> >
> >  void __weak arch_kexec_unprotect_crashkres(void)
> >  {}
> > +
> > +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> > +BTF_SET8_START(kexec_btf_ids)
> > +BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)
> > +BTF_SET8_END(kexec_btf_ids)
> > +
> > +static const struct btf_kfunc_id_set kexec_kfunc_set = {
> > +       .owner = THIS_MODULE,
> > +       .set   = &kexec_btf_ids,
> > +};
> > +
> > +static int __init crash_kfunc_init(void)
> > +{
> > +       register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &kexec_kfunc_set);
> > +       return 0;
> > +}
> > +
> > +subsys_initcall(crash_kfunc_init);
> > +#endif
> 
> It feels there will be a bunch of such boiler plate code
> in different .c files in many places in the kernel
> if we go with this approach.
> 
> Maybe we should do one call:
> register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING
> from kernel/bpf/helper.c
> to register all tracing kfuncs ?
> 
> And gate
> BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)
> with #ifdef CONFIG_KEXEC_CORE.
> 
> We have such a pattern in verifier.c already.

Good idea, thanks for the pointers. I'll do that in next version.

-- 
 Artem