On Thu, Jan 16, 2025 at 11:47 AM Juntong Deng <juntong.deng@xxxxxxxxxxx> wrote:
>
> This patch modifies SCX to use BPF capabilities.
>
> Make all SCX kfuncs register to BPF capabilities instead of
> BPF_PROG_TYPE_STRUCT_OPS.
>
> Add bpf_scx_bpf_capabilities_adjust as bpf_capabilities_adjust
> callback function.
>
> Signed-off-by: Juntong Deng <juntong.deng@xxxxxxxxxxx>
> ---
> kernel/sched/ext.c | 74 ++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 62 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 7fff1d045477..53cc7c3ed80b 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -5765,10 +5765,66 @@ bpf_scx_get_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> }
> }
'capabilities' name doesn't fit.
The word already has its meaning in the kernel.
It cannot be reused for a different purpose.
> +static int bpf_scx_bpf_capabilities_adjust(unsigned long *bpf_capabilities,
> + u32 context_info, bool enter)
> +{
> + if (enter) {
> + switch (context_info) {
> + case offsetof(struct sched_ext_ops, select_cpu):
> + ENABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_SELECT_CPU);
> + ENABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_ENQUEUE);
> + break;
> + case offsetof(struct sched_ext_ops, enqueue):
> + ENABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_ENQUEUE);
> + break;
> + case offsetof(struct sched_ext_ops, dispatch):
> + ENABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_DISPATCH);
> + break;
> + case offsetof(struct sched_ext_ops, running):
> + case offsetof(struct sched_ext_ops, stopping):
> + case offsetof(struct sched_ext_ops, enable):
> + ENABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_REST);
> + break;
> + case offsetof(struct sched_ext_ops, init):
> + case offsetof(struct sched_ext_ops, exit):
> + ENABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_UNLOCKED);
> + break;
> + default:
> + return -EINVAL;
> + }
> + } else {
> + switch (context_info) {
> + case offsetof(struct sched_ext_ops, select_cpu):
> + DISABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_SELECT_CPU);
> + DISABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_ENQUEUE);
> + break;
> + case offsetof(struct sched_ext_ops, enqueue):
> + DISABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_ENQUEUE);
> + break;
> + case offsetof(struct sched_ext_ops, dispatch):
> + DISABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_DISPATCH);
> + break;
> + case offsetof(struct sched_ext_ops, running):
> + case offsetof(struct sched_ext_ops, stopping):
> + case offsetof(struct sched_ext_ops, enable):
> + DISABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_REST);
> + break;
> + case offsetof(struct sched_ext_ops, init):
> + case offsetof(struct sched_ext_ops, exit):
> + DISABLE_BPF_CAPABILITY(bpf_capabilities, BPF_CAP_SCX_KF_UNLOCKED);
> + break;
> + default:
> + return -EINVAL;
> + }
> + }
> + return 0;
> +}
and this callback defeats the whole point of u32 bitmask.
In earlier patch
env->context_info = __btf_member_bit_offset(t, member) / 8; // moff
is also wrong.
The context_info name is too generic and misleading.
and 'env' isn't a right place to save moff.
Let's try to implement what was discussed earlier:
1
After successful check_struct_ops_btf_id() save moff in
prog->aux->attach_st_ops_member_off.
2
Add .filter callback to sched-ext kfunc registration path and
let it allow/deny kfuncs based on st_ops attach point.
3
Remove scx_kf_allow() and current->scx.kf_mask.
That will be a nice perf win and will prove that
this approach works end-to-end.
