From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta1.migadu.com (out-189.mta1.migadu.com [95.215.58.189]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D4CAA1FCFE7 for ; Mon, 14 Jul 2025 12:47:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752497239; cv=none; b=tXBV9TpUyWGyCSRANQ09KJlHm1OIuVyqBKqEyz5U1HAOy3MmKk11pu1Motyykb3ZXPIBUq9QqrSS4SPU3TzjX+vqTPG3v82gpXqKkEjuvhjsQtgtjiqh6+sZ8u21qlpC6StokULHHfK757e/3zvz+aTe5p9X7Nf0wOdZNPwFU6M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752497239; c=relaxed/simple; bh=prNXQRkRtUaVGj7/TXRpUFKmuQr8XWbiitiQiRG50Xk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=RtgFINYAO69j/Clcjk3ezmEA4ptSbhAXuYx24eOYnH64Ih/2qLg2vjr9vpJLK5WG0RdzlG6H+e/gAjlQhQ+N2RL3nq49DF19WzlBJjFq6CuM/2vQzDjd040Nz5UO4eTRshOKCzGfNp/HUt7/oQwYM40Cl5VRkputvSKCH3BeskI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ljFSGFAT; arc=none smtp.client-ip=95.215.58.189 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ljFSGFAT" Message-ID: <592129b2-0442-4b10-8b56-0e15d2ce113e@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1752497232; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=MV7LF13fTXZxj0A8E5XIBE9hIekvPavcj+pO/DVSFac=; b=ljFSGFATN5XOvGoeROXOU9IT/+RxQQW39xHV9rG98s8PZqIWWlDF/sD/CuLWjpQEkyjN1J WhgQ9Ewh46Y0imzVHgRiLzNzmMKnU0bUAyIyAL26Emh1m75PnKCsc0zD+MdcxhNf3Pv8a1 awFlq9WGWYLXQmtpxNg7qp/ZqaroM7U= Date: Mon, 14 Jul 2025 20:47:04 +0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [RFC PATCH bpf-next v2 1/3] bpf: Introduce BPF_F_CPU flag for percpu_array map To: Andrii Nakryiko Cc: bpf@vger.kernel.org, ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net References: <20250707160404.64933-1-leon.hwang@linux.dev> <20250707160404.64933-2-leon.hwang@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Leon Hwang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 2025/7/12 02:10, Andrii Nakryiko wrote: > On Mon, Jul 7, 2025 at 9:04 AM Leon Hwang wrote: >> >> This patch introduces support for the BPF_F_CPU flag in percpu_array maps >> to allow updating or looking up values for specified CPUs or for all CPUs >> with a single value. >> > > For next revision, please drop RFC tag, so this is tested and reviewed > as a proper patch set. > Sure. I'll drop it. >> This enhancement enables: >> >> * Efficient update of all CPUs using a single value when cpu == (u32)~0. >> * Targeted update or lookup for a specified CPU otherwise. >> >> The flag is passed via: >> >> * map_flags in bpf_percpu_array_update() along with embedded cpu field. >> * elem_flags in generic_map_update_batch() along with separated cpu field. >> >> Signed-off-by: Leon Hwang >> --- >> include/linux/bpf.h | 3 +- >> include/uapi/linux/bpf.h | 7 +++++ >> kernel/bpf/arraymap.c | 56 ++++++++++++++++++++++++++-------- >> kernel/bpf/syscall.c | 52 +++++++++++++++++++------------ >> tools/include/uapi/linux/bpf.h | 7 +++++ >> 5 files changed, 92 insertions(+), 33 deletions(-) >> > > [...] > >> >> + cpu = (u32)(flags >> 32); >> + flags &= (u32)~0; >> + if (unlikely(flags > BPF_F_CPU)) >> + return -EINVAL; >> + if (unlikely((flags & BPF_F_CPU) && cpu >= num_possible_cpus())) >> + return -E2BIG; >> + >> /* per_cpu areas are zero-filled and bpf programs can only >> * access 'value_size' of them, so copying rounded areas >> * will not leak any kernel data >> @@ -313,10 +320,15 @@ int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value) >> size = array->elem_size; >> rcu_read_lock(); >> pptr = array->pptrs[index & array->index_mask]; >> - for_each_possible_cpu(cpu) { >> - copy_map_value_long(map, value + off, per_cpu_ptr(pptr, cpu)); >> - check_and_init_map_value(map, value + off); >> - off += size; >> + if (flags & BPF_F_CPU) { >> + copy_map_value_long(map, value, per_cpu_ptr(pptr, cpu)); >> + check_and_init_map_value(map, value); >> + } else { >> + for_each_possible_cpu(cpu) { >> + copy_map_value_long(map, value + off, per_cpu_ptr(pptr, cpu)); >> + check_and_init_map_value(map, value + off); >> + off += size; >> + } >> } >> rcu_read_unlock(); >> return 0; >> @@ -387,13 +399,21 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value, >> struct bpf_array *array = container_of(map, struct bpf_array, map); >> u32 index = *(u32 *)key; >> void __percpu *pptr; >> - int cpu, off = 0; >> - u32 size; >> + bool reuse_value; >> + u32 size, cpu; >> + int off = 0; >> >> - if (unlikely(map_flags > BPF_EXIST)) >> + cpu = (u32)(map_flags >> 32); >> + map_flags = map_flags & (u32)~0; > > be consistent, use &= approach as above > Ack. >> + if (unlikely(map_flags > BPF_F_CPU)) >> /* unknown flags */ >> return -EINVAL; >> >> + if (unlikely((map_flags & BPF_F_CPU) && cpu != BPF_ALL_CPUS && >> + cpu >= num_possible_cpus())) >> + /* invalid cpu */ >> + return -E2BIG; >> + >> if (unlikely(index >= array->map.max_entries)) >> /* all elements were pre-allocated, cannot insert a new one */ >> return -E2BIG; >> @@ -409,12 +429,22 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value, >> * so no kernel data leaks possible >> */ >> size = array->elem_size; >> + reuse_value = (map_flags & BPF_F_CPU) && cpu == BPF_ALL_CPUS; > > I find "reuse_value" name extremely misleading, I stumble upon this > every time (because "value" is ambiguous, is it the source value or > map value we are updating?). Please drop it, there is no need for it, > just do `map_flags & BPF_F_CPU` check in that for_each_possible_cpu > loop below > Ack. >> rcu_read_lock(); >> pptr = array->pptrs[index & array->index_mask]; >> - for_each_possible_cpu(cpu) { >> - copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value + off); >> + if ((map_flags & BPF_F_CPU) && cpu != BPF_ALL_CPUS) { >> + copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value); >> bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu)); >> - off += size; >> + } else { >> + for_each_possible_cpu(cpu) { >> + if (!reuse_value) { >> + copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value + off); >> + off += size; >> + } else { >> + copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value); >> + } > > simpler and less duplication: > > copy_map_value_long(map, per_cpu_ptr(pptr, cpu), value + off); > /* > * same user-provided value is used if BPF_F_CPU is specified, > * otherwise value is an array of per-cpu values > */ > if (!(map_flags & BPF_F_CPU)) > off += size; > LGTM. >> + bpf_obj_free_fields(array->map.record, per_cpu_ptr(pptr, cpu)); >> + } >> } >> rcu_read_unlock(); >> return 0; >> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c >> index 7db7182a3057..a3ce0cdecb3c 100644 >> --- a/kernel/bpf/syscall.c >> +++ b/kernel/bpf/syscall.c >> @@ -129,8 +129,12 @@ bool bpf_map_write_active(const struct bpf_map *map) >> return atomic64_read(&map->writecnt) != 0; >> } >> >> -static u32 bpf_map_value_size(const struct bpf_map *map) >> +static u32 bpf_map_value_size(const struct bpf_map *map, u64 flags) >> { >> + if ((flags & BPF_F_CPU) && >> + map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) > > formatting is off, keep single line > Ack. >> + return round_up(map->value_size, 8); >> + >> if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH || >> map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH || >> map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY || >> @@ -312,7 +316,7 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value, >> map->map_type == BPF_MAP_TYPE_LRU_PERCPU_HASH) { >> err = bpf_percpu_hash_copy(map, key, value); >> } else if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) { >> - err = bpf_percpu_array_copy(map, key, value); >> + err = bpf_percpu_array_copy(map, key, value, flags); >> } else if (map->map_type == BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE) { >> err = bpf_percpu_cgroup_storage_copy(map, key, value); >> } else if (map->map_type == BPF_MAP_TYPE_STACK_TRACE) { >> @@ -1662,7 +1666,7 @@ static int map_lookup_elem(union bpf_attr *attr) >> if (CHECK_ATTR(BPF_MAP_LOOKUP_ELEM)) >> return -EINVAL; >> >> - if (attr->flags & ~BPF_F_LOCK) >> + if ((attr->flags & (u32)~0) & ~(BPF_F_LOCK | BPF_F_CPU)) > > nit: this whole `attr->flags & (u32)~0` looks like an over-engineered > `(u32)attr->flags`... > >> return -EINVAL; > > we should probably also have a condition checking that upper 32 bits > are zero if BPF_F_CPU is not set? > Correct. We should check the upper 32 bits if BPF_F_CPU is not set. It should check the flags like `(attr->flags & ~BPF_F_LOCK) && !(attr->flags & BPF_F_CPU)`. >> >> CLASS(fd, f)(attr->map_fd); >> @@ -1680,7 +1684,7 @@ static int map_lookup_elem(union bpf_attr *attr) >> if (IS_ERR(key)) >> return PTR_ERR(key); >> >> - value_size = bpf_map_value_size(map); >> + value_size = bpf_map_value_size(map, attr->flags); >> >> err = -ENOMEM; >> value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN); >> @@ -1749,7 +1753,7 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr) >> goto err_put; >> } >> >> - value_size = bpf_map_value_size(map); >> + value_size = bpf_map_value_size(map, attr->flags); >> value = kvmemdup_bpfptr(uvalue, value_size); >> if (IS_ERR(value)) { >> err = PTR_ERR(value); >> @@ -1941,19 +1945,25 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file, >> { >> void __user *values = u64_to_user_ptr(attr->batch.values); >> void __user *keys = u64_to_user_ptr(attr->batch.keys); >> - u32 value_size, cp, max_count; >> + u32 value_size, cp, max_count, cpu = attr->batch.cpu; >> + u64 elem_flags = attr->batch.elem_flags; >> void *key, *value; >> int err = 0; >> >> - if (attr->batch.elem_flags & ~BPF_F_LOCK) >> + if (elem_flags & ~(BPF_F_LOCK | BPF_F_CPU)) >> return -EINVAL; >> >> - if ((attr->batch.elem_flags & BPF_F_LOCK) && >> + if ((elem_flags & BPF_F_LOCK) && >> !btf_record_has_field(map->record, BPF_SPIN_LOCK)) { >> return -EINVAL; >> } >> >> - value_size = bpf_map_value_size(map); >> + if ((elem_flags & BPF_F_CPU) && >> + map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY) >> + return -EINVAL; >> + >> + value_size = bpf_map_value_size(map, elem_flags); >> + elem_flags = (((u64)cpu) << 32) | elem_flags; > > nit: elem_flags |= (u64)cpu << 32; > > same effect, but a bit more explicitly stating "we are just adding > stuff to elem_flags" > Ack. >> >> max_count = attr->batch.count; >> if (!max_count) >> @@ -1979,8 +1989,7 @@ int generic_map_update_batch(struct bpf_map *map, struct file *map_file, >> copy_from_user(value, values + cp * value_size, value_size)) >> break; >> >> - err = bpf_map_update_value(map, map_file, key, value, >> - attr->batch.elem_flags); >> + err = bpf_map_update_value(map, map_file, key, value, elem_flags); >> >> if (err) >> break; >> @@ -2004,18 +2013,24 @@ int generic_map_lookup_batch(struct bpf_map *map, >> void __user *ubatch = u64_to_user_ptr(attr->batch.in_batch); >> void __user *values = u64_to_user_ptr(attr->batch.values); >> void __user *keys = u64_to_user_ptr(attr->batch.keys); >> + u32 value_size, cp, max_count, cpu = attr->batch.cpu; >> void *buf, *buf_prevkey, *prev_key, *key, *value; >> - u32 value_size, cp, max_count; >> + u64 elem_flags = attr->batch.elem_flags; >> int err; >> >> - if (attr->batch.elem_flags & ~BPF_F_LOCK) >> + if (elem_flags & ~(BPF_F_LOCK | BPF_F_CPU)) >> return -EINVAL; >> >> - if ((attr->batch.elem_flags & BPF_F_LOCK) && >> + if ((elem_flags & BPF_F_LOCK) && >> !btf_record_has_field(map->record, BPF_SPIN_LOCK)) >> return -EINVAL; >> >> - value_size = bpf_map_value_size(map); >> + if ((elem_flags & BPF_F_CPU) && >> + map->map_type != BPF_MAP_TYPE_PERCPU_ARRAY) >> + return -EINVAL; >> + >> + value_size = bpf_map_value_size(map, elem_flags); >> + elem_flags = (((u64)cpu) << 32) | elem_flags; >> > > ditto > Ack. >> max_count = attr->batch.count; >> if (!max_count) > > [...]