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([2600:1700:6cf8:1240::3b]) by smtp.gmail.com with ESMTPSA id i185-20020a37b8c2000000b0073b79edf46csm12507648qkf.83.2023.03.08.19.09.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Mar 2023 19:09:38 -0800 (PST) Message-ID: <4ed74470-f024-5019-230d-367d6733493f@gmail.com> Date: Wed, 8 Mar 2023 19:09:36 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH bpf-next v5 5/8] bpf: Update the struct_ops of a bpf_link. Content-Language: en-US, en-ZW To: Martin KaFai Lau , Kui-Feng Lee Cc: bpf@vger.kernel.org, ast@kernel.org, song@kernel.org, kernel-team@meta.com, andrii@kernel.org, sdf@google.com References: <20230308005050.255859-1-kuifeng@meta.com> <20230308005050.255859-6-kuifeng@meta.com> <5b760fdc-a3c2-f416-4729-c17e67f6b2d5@linux.dev> From: Kui-Feng Lee In-Reply-To: <5b760fdc-a3c2-f416-4729-c17e67f6b2d5@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 3/8/23 14:21, Martin KaFai Lau wrote: > On 3/7/23 4:50 PM, Kui-Feng Lee wrote: >> By improving the BPF_LINK_UPDATE command of bpf(), it should allow you >> to conveniently switch between different struct_ops on a single >> bpf_link. This would enable smoother transitions from one struct_ops >> to another. >> >> The struct_ops maps passing along with BPF_LINK_UPDATE should have the >> BPF_F_LINK flag. >> >> Signed-off-by: Kui-Feng Lee >> --- >>   include/linux/bpf.h            |  1 + >>   include/uapi/linux/bpf.h       |  8 ++++-- >>   kernel/bpf/bpf_struct_ops.c    | 46 ++++++++++++++++++++++++++++++++++ >>   kernel/bpf/syscall.c           | 43 ++++++++++++++++++++++++++++--- >>   tools/include/uapi/linux/bpf.h |  7 +++++- >>   5 files changed, 98 insertions(+), 7 deletions(-) >> >> diff --git a/include/linux/bpf.h b/include/linux/bpf.h >> index afca6c526fe4..29d555a82bad 100644 >> --- a/include/linux/bpf.h >> +++ b/include/linux/bpf.h >> @@ -1470,6 +1470,7 @@ struct bpf_link_ops { >>       void (*show_fdinfo)(const struct bpf_link *link, struct seq_file >> *seq); >>       int (*fill_link_info)(const struct bpf_link *link, >>                     struct bpf_link_info *info); >> +    int (*update_map)(struct bpf_link *link, struct bpf_map *new_map); >>   }; >>   struct bpf_tramp_link { >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >> index f9fc7b8af3c4..edef9cf7d596 100644 >> --- a/include/uapi/linux/bpf.h >> +++ b/include/uapi/linux/bpf.h >> @@ -1555,8 +1555,12 @@ union bpf_attr { >>       struct { /* struct used by BPF_LINK_UPDATE command */ >>           __u32        link_fd;    /* link fd */ >> -        /* new program fd to update link with */ >> -        __u32        new_prog_fd; >> +        union { >> +            /* new program fd to update link with */ >> +            __u32        new_prog_fd; >> +            /* new struct_ops map fd to update link with */ >> +            __u32           new_map_fd; >> +        }; >>           __u32        flags;        /* extra flags */ >>           /* expected link's program fd; is specified only if >>            * BPF_F_REPLACE flag is set in flags */ >> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c >> index 5a7e86cf67b5..79e663869e51 100644 >> --- a/kernel/bpf/bpf_struct_ops.c >> +++ b/kernel/bpf/bpf_struct_ops.c >> @@ -775,10 +775,56 @@ static int >> bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link, >>       return 0; >>   } >> +static int bpf_struct_ops_map_link_update(struct bpf_link *link, >> struct bpf_map *new_map) >> +{ >> +    struct bpf_struct_ops_value *kvalue; >> +    struct bpf_struct_ops_map *st_map, *old_st_map; >> +    struct bpf_struct_ops_link *st_link; >> +    struct bpf_map *old_map; >> +    int err = 0; >> + >> +    if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS || >> +        !(new_map->map_flags & BPF_F_LINK)) >> +        return -EINVAL; >> + >> +    mutex_lock(&update_mutex); >> + >> +    st_link = container_of(link, struct bpf_struct_ops_link, link); >> + >> +    /* The new and old struct_ops must be the same type. */ >> +    st_map = container_of(new_map, struct bpf_struct_ops_map, map); > > nit. move the st_link and st_map init out of the lock. > Ok >> + >> +    old_map = st_link->map; > > rcu_dereference_protected(...) > >> +    old_st_map = container_of(old_map, struct bpf_struct_ops_map, map); >> +    if (st_map->st_ops != old_st_map->st_ops || >> +        /* Pair with smp_store_release() during map_update */ >> +        smp_load_acquire(&st_map->kvalue.state) != >> BPF_STRUCT_OPS_STATE_READY) { > > nit. test the smp_load_acquire(&st_map...) outside of the lock. > Do it together with the new_map checking at the beginning of the func. Ok > >> +        err = -EINVAL; >> +        goto err_out; >> +    } >> + >> +    kvalue = &st_map->kvalue; >> + >> +    err = st_map->st_ops->update(kvalue->data, old_st_map->kvalue.data); >> +    if (err) >> +        goto err_out; >> + >> +    bpf_map_inc(new_map); >> +    rcu_assign_pointer(st_link->map, new_map); >> + >> +    bpf_map_put(old_map); >> + >> +err_out: >> +    mutex_unlock(&update_mutex); >> + >> +    return err; >> +} >> + >>   static const struct bpf_link_ops bpf_struct_ops_map_lops = { >>       .dealloc = bpf_struct_ops_map_link_dealloc, >>       .show_fdinfo = bpf_struct_ops_map_link_show_fdinfo, >>       .fill_link_info = bpf_struct_ops_map_link_fill_link_info, >> +    .update_map = bpf_struct_ops_map_link_update, >>   }; >>   int bpf_struct_ops_link_create(union bpf_attr *attr) >> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c >> index 3a4503987a48..c087dd2e2c08 100644 >> --- a/kernel/bpf/syscall.c >> +++ b/kernel/bpf/syscall.c >> @@ -4658,6 +4658,30 @@ static int link_create(union bpf_attr *attr, >> bpfptr_t uattr) >>       return ret; >>   } >> +static int link_update_map(struct bpf_link *link, union bpf_attr *attr) >> +{ >> +    struct bpf_map *new_map; >> +    int ret = 0; >> + >> +    new_map = bpf_map_get(attr->link_update.new_map_fd); >> +    if (IS_ERR(new_map)) >> +        return -EINVAL; >> + >> +    if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS) { > > This is unnecessary test. The individual '.update_map()' should test for > its own map_type and the new bpf_struct_ops_map_link_update() does test it. > Will remove it. >> +        ret = -EINVAL; >> +        goto out_put_map; >> +    } >> + >> +    if (link->ops->update_map) > > This has just been tested in link_update() before calling > link_update_map(). Sure > >> +        ret = link->ops->update_map(link, new_map); >> +    else >> +        ret = -EINVAL; >> + >> +out_put_map: >> +    bpf_map_put(new_map); >> +    return ret; >> +} >> + >>   #define BPF_LINK_UPDATE_LAST_FIELD link_update.old_prog_fd >>   static int link_update(union bpf_attr *attr) >> @@ -4670,14 +4694,25 @@ static int link_update(union bpf_attr *attr) >>       if (CHECK_ATTR(BPF_LINK_UPDATE)) >>           return -EINVAL; >> -    flags = attr->link_update.flags; >> -    if (flags & ~BPF_F_REPLACE) >> -        return -EINVAL; >> - >>       link = bpf_link_get_from_fd(attr->link_update.link_fd); >>       if (IS_ERR(link)) >>           return PTR_ERR(link); >> +    flags = attr->link_update.flags; >> + >> +    if (link->ops->update_map) { >> +        if (flags)    /* always replace the existing one */ >> +            ret = -EINVAL; >> +        else >> +            ret = link_update_map(link, attr); >> +        goto out_put_link; >> +    } >> + >> +    if (flags & ~BPF_F_REPLACE) { >> +        ret = -EINVAL; >> +        goto out_put_link; >> +    } >> + >>       new_prog = bpf_prog_get(attr->link_update.new_prog_fd); >>       if (IS_ERR(new_prog)) { >>           ret = PTR_ERR(new_prog); >