Re: [PATCH bpf-next v3 2/3] bpf: struct_ops supports more than one page for trampolines.

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On 2/23/24 7:03 PM, Kui-Feng Lee wrote:
+static void bpf_struct_ops_map_free_image(struct bpf_struct_ops_map *st_map)
+{
+	int i;
+	void *image;
+
+	bpf_jit_uncharge_modmem(PAGE_SIZE * st_map->image_pages_cnt);
+	for (i = 0; i < st_map->image_pages_cnt; i++) {
+		image = st_map->image_pages[i];
+		arch_free_bpf_trampoline(image, PAGE_SIZE);
+	}
+	st_map->image_pages_cnt = 0;
+}
+

[ ... ]

@@ -133,7 +128,8 @@ int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,
  	err = bpf_struct_ops_prepare_trampoline(tlinks, link,
  						&st_ops->func_models[op_idx],
  						&dummy_ops_test_ret_function,
-						image, image + PAGE_SIZE);
+						&image, &image_off,
+						true);
  	if (err < 0)
  		goto out;
@@ -147,6 +143,8 @@ int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,
  		err = -EFAULT;
  out:
  	kfree(args);
+	if (image)
+		bpf_jit_uncharge_modmem(PAGE_SIZE);
  	arch_free_bpf_trampoline(image, PAGE_SIZE);

It seems my last reply on v2 has crossed over with v3.

The bpf_struct_ops_free_trampoline() highlighted in my last reply should
address your concern in v2 that the caller needs to remember
the bpf_jit_uncharge_modmem here.

I think the trampoline alloc(aka prepare here)/free pair that you also
suggested in v2 discussion is a nice match here and work as a
charge+alloc and uncharge+free pair.

  	if (link)
  		bpf_link_put(&link->link);





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