Re: [PATCH bpf-next v3 3/5] bpf: Mark each subprog with proper pstack states

[Yonghong Song <yonghong.song@linux.dev>]

On 9/30/24 7:49 AM, Alexei Starovoitov wrote:
> On Thu, Sep 26, 2024 at 4:45 PM Yonghong Song <yonghong.song@linux.dev> wrote:
>> Three private stack states are used to direct jit action:
>>    PSTACK_TREE_NO:       do not use private stack
>>    PSTACK_TREE_INTERNAL: adjust frame pointer address (similar to normal stack)
>>    PSTACK_TREE_ROOT:     set the frame pointer
>>
>> Note that for subtree root, even if the root bpf_prog stack size is 0,
>> PSTACK_TREE_INTERNAL is still used. This is for bpf exception handling.
>> More details can be found in subsequent jit support and selftest patches.
>>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
>> ---
>>   include/linux/bpf.h   |  9 +++++++++
>>   kernel/bpf/core.c     | 19 +++++++++++++++++++
>>   kernel/bpf/verifier.c | 30 ++++++++++++++++++++++++++++++
>>   3 files changed, 58 insertions(+)
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 156b9516d9f6..8f02d11bd408 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1550,6 +1550,12 @@ struct bpf_prog_aux {
>>          };
>>   };
>>
>> +enum bpf_pstack_state {
>> +       PSTACK_TREE_NO,
>> +       PSTACK_TREE_INTERNAL,
>> +       PSTACK_TREE_ROOT,
>> +};
> The names could be improved and 'state' doesn't quite fit imo.
> How about:
> enum bpf_priv_stack_mode {
>     NO_PRIV_STACK,
>     PRIV_STACK_SUB_PROG,
>     PRIV_STACK_MAIN_PROG,
> };

Since we agreed to use priv_stack instead of pstack. The above
names make sense. Will change.

>
>> +
>>   struct bpf_prog {
>>          u16                     pages;          /* Number of allocated pages */
>>          u16                     jited:1,        /* Is our filter JIT'ed? */
>> @@ -1570,15 +1576,18 @@ struct bpf_prog {
>>                                  pstack_eligible:1; /* Candidate for private stacks */
>>          enum bpf_prog_type      type;           /* Type of BPF program */
>>          enum bpf_attach_type    expected_attach_type; /* For some prog types */
>> +       enum bpf_pstack_state   pstack:2;       /* Private stack state */
>>          u32                     len;            /* Number of filter blocks */
>>          u32                     jited_len;      /* Size of jited insns in bytes */
>>          u8                      tag[BPF_TAG_SIZE];
>> +       u16                     subtree_stack_depth; /* Subtree stack depth if PSTACK_TREE_ROOT prog, 0 otherwise */
> All the extra vars can be in prog->aux.
> No need to put them in struct bpf_prog.

Will do.

>
>>          struct bpf_prog_stats __percpu *stats;
>>          int __percpu            *active;
>>          unsigned int            (*bpf_func)(const void *ctx,
>>                                              const struct bpf_insn *insn);
>>          struct bpf_prog_aux     *aux;           /* Auxiliary fields */
>>          struct sock_fprog_kern  *orig_prog;     /* Original BPF program */
>> +       void __percpu           *private_stack_ptr;
> same as this one. prog->aux should be fine.

Will do.

>
>>          /* Instructions for interpreter */
>>          union {
>>                  DECLARE_FLEX_ARRAY(struct sock_filter, insns);
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 0727fff6de0e..d6eb052f6631 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -1239,6 +1239,7 @@ void __weak bpf_jit_free(struct bpf_prog *fp)
>>                  struct bpf_binary_header *hdr = bpf_jit_binary_hdr(fp);
>>
>>                  bpf_jit_binary_free(hdr);
>> +               free_percpu(fp->private_stack_ptr);
>>                  WARN_ON_ONCE(!bpf_prog_kallsyms_verify_off(fp));
>>          }
>>
>> @@ -2420,6 +2421,24 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
>>                  if (*err)
>>                          return fp;
>>
>> +               if (fp->pstack_eligible) {
>> +                       if (!fp->aux->stack_depth) {
>> +                               fp->pstack = PSTACK_TREE_NO;
>> +                       } else {
>> +                               void __percpu *private_stack_ptr;
>> +
>> +                               fp->pstack = PSTACK_TREE_ROOT;
>> +                               private_stack_ptr =
>> +                                       __alloc_percpu_gfp(fp->aux->stack_depth, 8, GFP_KERNEL);
>> +                               if (!private_stack_ptr) {
>> +                                       *err = -ENOMEM;
>> +                                       return fp;
>> +                               }
>> +                               fp->subtree_stack_depth = fp->aux->stack_depth;
>> +                               fp->private_stack_ptr = private_stack_ptr;
>> +                       }
>> +               }
>> +
>>                  fp = bpf_int_jit_compile(fp);
>>                  bpf_prog_jit_attempt_done(fp);
>>                  if (!fp->jited && jit_needed) {
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 69e17cb22037..9d093e2013ca 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -20060,6 +20060,7 @@ static int jit_subprogs(struct bpf_verifier_env *env)
>>   {
>>          struct bpf_prog *prog = env->prog, **func, *tmp;
>>          int i, j, subprog_start, subprog_end = 0, len, subprog;
>> +       int subtree_top_idx, subtree_stack_depth;
>>          struct bpf_map *map_ptr;
>>          struct bpf_insn *insn;
>>          void *old_bpf_func;
>> @@ -20138,6 +20139,35 @@ static int jit_subprogs(struct bpf_verifier_env *env)
>>                  func[i]->is_func = 1;
>>                  func[i]->sleepable = prog->sleepable;
>>                  func[i]->aux->func_idx = i;
>> +
>> +               subtree_top_idx = env->subprog_info[i].subtree_top_idx;
>> +               if (env->subprog_info[subtree_top_idx].pstack_eligible) {
>> +                       if (subtree_top_idx == i)
>> +                               func[i]->subtree_stack_depth =
>> +                                       env->subprog_info[i].subtree_stack_depth;
>> +
>> +                       subtree_stack_depth = func[i]->subtree_stack_depth;
>> +                       if (subtree_top_idx != i) {
>> +                               if (env->subprog_info[subtree_top_idx].subtree_stack_depth)
>> +                                       func[i]->pstack = PSTACK_TREE_INTERNAL;
>> +                               else
>> +                                       func[i]->pstack = PSTACK_TREE_NO;
>> +                       } else if (!subtree_stack_depth) {
>> +                               func[i]->pstack = PSTACK_TREE_INTERNAL;
>> +                       } else {
>> +                               void __percpu *private_stack_ptr;
>> +
>> +                               func[i]->pstack = PSTACK_TREE_ROOT;
>> +                               private_stack_ptr =
>> +                                       __alloc_percpu_gfp(subtree_stack_depth, 8, GFP_KERNEL);
>> +                               if (!private_stack_ptr) {
>> +                                       err = -ENOMEM;
>> +                                       goto out_free;
>> +                               }
>> +                               func[i]->private_stack_ptr = private_stack_ptr;
>> +                       }
>> +               }
>> +
>>                  /* Below members will be freed only at prog->aux */
>>                  func[i]->aux->btf = prog->aux->btf;
>>                  func[i]->aux->func_info = prog->aux->func_info;
>> --
>> 2.43.5
>>