Re: [PATCH bpf-next v2 2/3] bpf: struct_ops supports more than one page for trampolines.

[Martin KaFai Lau <martin.lau@xxxxxxxxx>]

On 2/23/24 10:29 AM, Kui-Feng Lee wrote:
> One thing I forgot to mention is that bpf_dummy_ops has to call
> bpf_jit_uncharge_modmem(PAGE_SIZE) as well. The other option is to move
> bpf_jit_charge_modmem() out of bpf_struct_ops_prepare_trampoline(),
> meaning bpf_struct_ops_map_update_elem() should handle the case that the
> allocation in bpf_struct_ops_prepare_trampoline() successes, but
> bpf_jit_charge_modmem() fails.

Keep the charge/uncharge in bpf_struct_ops_prepare_trampoline().

It is fine to have bpf_dummy_ops charge and then uncharge a PAGE_SIZE. There is 
no need to optimize for bpf_dummy_ops. Use bpf_struct_ops_free_trampoline() in 
bpf_dummy_ops to uncharge and free.


> > > void bpf_struct_ops_free_trampoline(void *image)
> > > {
> > >      bpf_jit_uncharge_modmem(PAGE_SIZE);
> > >      arch_free_bpf_trampoline(image, PAGE_SIZE);
> > > }