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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Hao Luo <haoluo@google.com>
Cc: Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>, Shuah Khan <shuah@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andriin@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Quentin Monnet <quentin@isovalent.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>, Andrey Ignatov <rdna@fb.com>,
	Jakub Sitnicki <jakub@cloudflare.com>
Subject: Re: [PATCH bpf-next v1 6/8] bpf: Introduce bpf_per_cpu_ptr()
Date: Fri, 21 Aug 2020 20:31:39 -0700	[thread overview]
Message-ID: <CAEf4BzZ+uqE73tM6W1vXyc-hu6fB8B9ZNniq-XHYhFDjhHg9gA@mail.gmail.com> (raw)
In-Reply-To: <CAEf4BzZY2LyJvF9HCdAzHM7WG26GO0qqX=Wc6EiXArks=kmazA@mail.gmail.com>

On Fri, Aug 21, 2020 at 8:26 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Wed, Aug 19, 2020 at 3:42 PM Hao Luo <haoluo@google.com> wrote:
> >
> > Add bpf_per_cpu_ptr() to help bpf programs access percpu vars.
> > bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the kernel
> > except that it may return NULL. This happens when the cpu parameter is
> > out of range. So the caller must check the returned value.
> >
> > Signed-off-by: Hao Luo <haoluo@google.com>
> > ---
>
> The logic looks correct, few naming nits, but otherwise:
>
> Acked-by: Andrii Nakryiko <andriin@fb.com>
>
> >  include/linux/bpf.h      |  3 ++
> >  include/linux/btf.h      | 11 +++++++
> >  include/uapi/linux/bpf.h | 14 +++++++++
> >  kernel/bpf/btf.c         | 10 -------
> >  kernel/bpf/verifier.c    | 64 ++++++++++++++++++++++++++++++++++++++--
> >  kernel/trace/bpf_trace.c | 18 +++++++++++
> >  6 files changed, 107 insertions(+), 13 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 55f694b63164..613404beab33 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -268,6 +268,7 @@ enum bpf_arg_type {
> >         ARG_PTR_TO_ALLOC_MEM,   /* pointer to dynamically allocated memory */
> >         ARG_PTR_TO_ALLOC_MEM_OR_NULL,   /* pointer to dynamically allocated memory or NULL */
> >         ARG_CONST_ALLOC_SIZE_OR_ZERO,   /* number of allocated bytes requested */
> > +       ARG_PTR_TO_PERCPU_BTF_ID,       /* pointer to in-kernel percpu type */
> >  };
> >
> >  /* type of values returned from helper functions */
> > @@ -281,6 +282,7 @@ enum bpf_return_type {
> >         RET_PTR_TO_SOCK_COMMON_OR_NULL, /* returns a pointer to a sock_common or NULL */
> >         RET_PTR_TO_ALLOC_MEM_OR_NULL,   /* returns a pointer to dynamically allocated memory or NULL */
> >         RET_PTR_TO_BTF_ID_OR_NULL,      /* returns a pointer to a btf_id or NULL */
> > +       RET_PTR_TO_MEM_OR_BTF_OR_NULL,  /* returns a pointer to a valid memory or a btf_id or NULL */
>
> I know it's already very long, but still let's use BTF_ID consistently
>
> >  };
> >
> >  /* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs
> > @@ -360,6 +362,7 @@ enum bpf_reg_type {
> >         PTR_TO_RDONLY_BUF_OR_NULL, /* reg points to a readonly buffer or NULL */
> >         PTR_TO_RDWR_BUF,         /* reg points to a read/write buffer */
> >         PTR_TO_RDWR_BUF_OR_NULL, /* reg points to a read/write buffer or NULL */
> > +       PTR_TO_PERCPU_BTF_ID,    /* reg points to percpu kernel type */
> >  };
> >
>
> [...]
>
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 468376f2910b..c7e49a102ed2 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -3415,6 +3415,19 @@ union bpf_attr {
> >   *             A non-negative value equal to or less than *size* on success,
> >   *             or a negative error in case of failure.
> >   *
> > + * void *bpf_per_cpu_ptr(const void *ptr, u32 cpu)

btw, having bpf_this_cpu_ptr(const void *ptr) seems worthwhile as well, WDYT?

> > + *     Description
> > + *             Take the address of a percpu ksym and return a pointer pointing
> > + *             to the variable on *cpu*. A ksym is an extern variable decorated
> > + *             with '__ksym'. A ksym is percpu if there is a global percpu var
> > + *             (either static or global) defined of the same name in the kernel.
>
> The function signature has "ptr", not "ksym", but the description is
> using "ksym". please make them consistent (might name param
> "percpu_ptr")
>
> > + *
> > + *             bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the
> > + *             kernel, except that bpf_per_cpu_ptr() may return NULL. This
> > + *             happens if *cpu* is larger than nr_cpu_ids. The caller of
> > + *             bpf_per_cpu_ptr() must check the returned value.
> > + *     Return
> > + *             A generic pointer pointing to the variable on *cpu*.
> >   */
>
> [...]
>
> > +       } else if (arg_type == ARG_PTR_TO_PERCPU_BTF_ID) {
> > +               expected_type = PTR_TO_PERCPU_BTF_ID;
> > +               if (type != expected_type)
> > +                       goto err_type;
> > +               if (!reg->btf_id) {
> > +                       verbose(env, "Helper has zero btf_id in R%d\n", regno);
>
> nit: "invalid btf_id"?
>
> > +                       return -EACCES;
> > +               }
> > +               meta->ret_btf_id = reg->btf_id;
> >         } else if (arg_type == ARG_PTR_TO_BTF_ID) {
> >                 expected_type = PTR_TO_BTF_ID;
> >                 if (type != expected_type)
> > @@ -4904,6 +4918,30 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
> >                 regs[BPF_REG_0].type = PTR_TO_MEM_OR_NULL;
> >                 regs[BPF_REG_0].id = ++env->id_gen;
> >                 regs[BPF_REG_0].mem_size = meta.mem_size;
>
> [...]

  reply	other threads:[~2020-08-22  3:31 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-19 22:40 [PATCH bpf-next v1 0/8] bpf: BTF support for ksyms Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 1/8] bpf: Introduce pseudo_btf_id Hao Luo
2020-08-20 15:22   ` Yonghong Song
2020-08-20 17:04     ` Hao Luo
2020-08-25  0:05     ` Hao Luo
2020-08-25  0:43       ` Yonghong Song
2020-08-20 16:43   ` Yonghong Song
2020-08-20 21:53   ` Alexei Starovoitov
2020-08-21  2:22     ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 2/8] bpf: Propagate BPF_PSEUDO_BTF_ID to uapi headers in /tools Hao Luo
2020-08-20 16:44   ` Yonghong Song
2020-08-19 22:40 ` [PATCH bpf-next v1 3/8] bpf: Introduce help function to validate ksym's type Hao Luo
2020-08-20 17:20   ` Yonghong Song
2020-08-21 21:50     ` Andrii Nakryiko
2020-08-22  0:43       ` Hao Luo
2020-08-22  2:43         ` Andrii Nakryiko
2020-08-22  7:04           ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 4/8] bpf/libbpf: BTF support for typed ksyms Hao Luo
2020-08-21 22:37   ` Andrii Nakryiko
2020-08-27 22:29     ` Hao Luo
2020-09-01 18:11       ` Andrii Nakryiko
2020-09-01 20:35         ` Hao Luo
2020-09-01 23:54           ` Andrii Nakryiko
2020-09-02  0:46             ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 5/8] bpf/selftests: ksyms_btf to test " Hao Luo
2020-08-20 17:28   ` Yonghong Song
2020-08-21 23:03     ` Andrii Nakryiko
2020-08-22  7:26       ` Hao Luo
2020-08-22  7:35         ` Andrii Nakryiko
2020-08-19 22:40 ` [PATCH bpf-next v1 6/8] bpf: Introduce bpf_per_cpu_ptr() Hao Luo
2020-08-22  3:26   ` Andrii Nakryiko
2020-08-22  3:31     ` Andrii Nakryiko [this message]
2020-08-22  7:49       ` Hao Luo
2020-08-22  7:55         ` Andrii Nakryiko
2020-08-25  1:03           ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 7/8] bpf: Propagate bpf_per_cpu_ptr() to /tools Hao Luo
2020-08-20 17:30   ` Yonghong Song
2020-08-19 22:40 ` [PATCH bpf-next v1 8/8] bpf/selftests: Test for bpf_per_cpu_ptr() Hao Luo
2020-08-22  3:30   ` Andrii Nakryiko
2020-08-28  3:42     ` Hao Luo
2020-09-01 18:12       ` Andrii Nakryiko
2020-09-01 19:47         ` Hao Luo

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