From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (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 C22593174D for ; Thu, 18 Jan 2024 22:27:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705616852; cv=none; b=Bsth05tOeCdTAPjuBdMBQFIzR60EWqYNdVZc/2iezfKdLmImhbz67w6XpeaKMDRTmXeiTDzWFoUUGKFiJ8aa53XGxxMeGCUKbm0Xd9nlF9TFPrehHttzjVIDd4noDGkMTteJ4aJJWdM8KzyiTv6/JepD2ssVhsfoYzl1jxAeL7k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705616852; c=relaxed/simple; bh=a8Zd+7iE7jv872u6vNL4SPCa9yJG/pYGRTjmPeHPBhk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=J5aP5k3dfny36sguR3F7hYVmoEfhezz+a1C+ckV1IFtFBTlW+EW5tCy50dcH0qR3Uk1eivHBE02inAocS9EVozK1G4rt0fi+uPi3OWFh9SDb9fgcfxMg/n1PgwED0JRKj9mIkv00P/oq947gcqozkW1JKx3JptMZo//lvNG46Hg= 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=Okm1CRMX; arc=none smtp.client-ip=95.215.58.188 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="Okm1CRMX" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1705616849; 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=i8YY1BNIvEeUzIa8KrkaLTZLdSwaSV9jEiSxqA/hNKY=; b=Okm1CRMXY7Ze5CBIMwJY+Kn5TmHlD9i63nZK2Y4FTbNRxvY6l9pCB1sK2hhMdY+xhRIwBn Wkqt+iMmLoyi68KqbmsUzfZexFmMvN/8EWXwUmZv+IRilo41VNsJEzvq9nGlkufq/oZt1Z YUTNo3lg5sMgvxbgGTOgeGAF8QuoYEg= Date: Thu, 18 Jan 2024 14:27:22 -0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v3 bpf-next 1/3] bpf: Add bpf_iter_cpumask kfuncs Content-Language: en-GB To: Yafang Shao , ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, tj@kernel.org Cc: bpf@vger.kernel.org, lkp@intel.com References: <20240117024823.4186-1-laoar.shao@gmail.com> <20240117024823.4186-2-laoar.shao@gmail.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20240117024823.4186-2-laoar.shao@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 1/16/24 6:48 PM, Yafang Shao wrote: > Add three new kfuncs for bpf_iter_cpumask. > - bpf_iter_cpumask_new > It is defined with KF_RCU_PROTECTED and KF_RCU. > KF_RCU_PROTECTED is defined because we must use it under the > protection of RCU. > KF_RCU is defined because the cpumask must be a RCU trusted pointer > such as task->cpus_ptr. I am not sure whether we need both or not. KF_RCU_PROTECTED means the function call needs within the rcu cs. KF_RCU means the argument usage needs within the rcu cs. We only need one of them (preferrably KF_RCU). > - bpf_iter_cpumask_next > - bpf_iter_cpumask_destroy > > These new kfuncs facilitate the iteration of percpu data, such as > runqueues, psi_cgroup_cpu, and more. > > Signed-off-by: Yafang Shao > --- > kernel/bpf/cpumask.c | 69 ++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 69 insertions(+) > > diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c > index 2e73533a3811..1840e48e6142 100644 > --- a/kernel/bpf/cpumask.c > +++ b/kernel/bpf/cpumask.c > @@ -422,6 +422,72 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask) > return cpumask_weight(cpumask); > } > > +struct bpf_iter_cpumask { > + __u64 __opaque[2]; > +} __aligned(8); > + > +struct bpf_iter_cpumask_kern { > + const struct cpumask *mask; > + int cpu; > +} __aligned(8); > + > +/** > + * bpf_iter_cpumask_new() - Create a new bpf_iter_cpumask for a specified cpumask > + * @it: The new bpf_iter_cpumask to be created. > + * @mask: The cpumask to be iterated over. > + * > + * This function initializes a new bpf_iter_cpumask structure for iterating over > + * the specified CPU mask. It assigns the provided cpumask to the newly created > + * bpf_iter_cpumask @it for subsequent iteration operations. > + * > + * On success, 0 is returen. On failure, ERR is returned. > + */ > +__bpf_kfunc int bpf_iter_cpumask_new(struct bpf_iter_cpumask *it, const struct cpumask *mask) > +{ > + struct bpf_iter_cpumask_kern *kit = (void *)it; > + > + BUILD_BUG_ON(sizeof(struct bpf_iter_cpumask_kern) > sizeof(struct bpf_iter_cpumask)); > + BUILD_BUG_ON(__alignof__(struct bpf_iter_cpumask_kern) != > + __alignof__(struct bpf_iter_cpumask)); > + > + kit->mask = mask; > + kit->cpu = -1; > + return 0; > +} We have problem here. Let us say bpf_iter_cpumask_new() is called inside rcu cs. Once the control goes out of rcu cs, 'mask' could be freed, right? Or you require bpf_iter_cpumask_next() needs to be in the same rcu cs as bpf_iter_cpumask_new(). But such a requirement seems odd. I think we can do things similar to bpf_iter_task_vma. You can allocate memory with bpf_mem_alloc() in bpf_iter_cpumask_new() to keep a copy of mask. This way, you do not need to worry about potential use-after-free issue. The memory can be freed with bpf_iter_cpumask_destroy(). > + > +/** > + * bpf_iter_cpumask_next() - Get the next CPU in a bpf_iter_cpumask > + * @it: The bpf_iter_cpumask > + * > + * This function retrieves a pointer to the number of the next CPU within the > + * specified bpf_iter_cpumask. It allows sequential access to CPUs within the > + * cpumask. If there are no further CPUs available, it returns NULL. > + * > + * Returns a pointer to the number of the next CPU in the cpumask or NULL if no > + * further CPUs. > + */ > +__bpf_kfunc int *bpf_iter_cpumask_next(struct bpf_iter_cpumask *it) > +{ > + struct bpf_iter_cpumask_kern *kit = (void *)it; > + const struct cpumask *mask = kit->mask; > + int cpu; > + > + cpu = cpumask_next(kit->cpu, mask); > + if (cpu >= nr_cpu_ids) > + return NULL; > + > + kit->cpu = cpu; > + return &kit->cpu; > +} > + > +/** > + * bpf_iter_cpumask_destroy() - Destroy a bpf_iter_cpumask > + * @it: The bpf_iter_cpumask to be destroyed. > + */ > +__bpf_kfunc void bpf_iter_cpumask_destroy(struct bpf_iter_cpumask *it) > +{ > +} > + > __bpf_kfunc_end_defs(); > > BTF_SET8_START(cpumask_kfunc_btf_ids) > @@ -450,6 +516,9 @@ BTF_ID_FLAGS(func, bpf_cpumask_copy, KF_RCU) > BTF_ID_FLAGS(func, bpf_cpumask_any_distribute, KF_RCU) > BTF_ID_FLAGS(func, bpf_cpumask_any_and_distribute, KF_RCU) > BTF_ID_FLAGS(func, bpf_cpumask_weight, KF_RCU) > +BTF_ID_FLAGS(func, bpf_iter_cpumask_new, KF_ITER_NEW | KF_RCU_PROTECTED | KF_RCU) > +BTF_ID_FLAGS(func, bpf_iter_cpumask_next, KF_ITER_NEXT | KF_RET_NULL) > +BTF_ID_FLAGS(func, bpf_iter_cpumask_destroy, KF_ITER_DESTROY) > BTF_SET8_END(cpumask_kfunc_btf_ids) > > static const struct btf_kfunc_id_set cpumask_kfunc_set = {