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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1766464930; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4sgm34XnAtjYqHmQ8m4pVVZ/fcJUWGruYJivSnP1OS4=; b=sZRbLbHAZYcVTrs1pZoM2rBFY8qzVAPKt8ffAlhBWRNomC+dxxlV9k7FfS7iik4lbVfYDH +dw5JRNuY2XOJPhrA2DEsyR039yQPD960Gd1cimG2vGSSt/RJQFmCKXOfZVp5q8fW4VJVO N3aLsOwhJ2m5xXkWuSR9DtfsvIR97V0= From: Roman Gushchin To: bpf@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: JP Kobryn , Alexei Starovoitov , Daniel Borkmann , Shakeel Butt , Michal Hocko , Johannes Weiner , Roman Gushchin Subject: [PATCH bpf-next v4 2/6] mm: introduce BPF kfuncs to deal with memcg pointers Date: Mon, 22 Dec 2025 20:41:52 -0800 Message-ID: <20251223044156.208250-3-roman.gushchin@linux.dev> In-Reply-To: <20251223044156.208250-1-roman.gushchin@linux.dev> References: <20251223044156.208250-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: 719E8100002 X-Rspamd-Server: rspam10 X-Stat-Signature: zzh4aitgtaczaq69qfoeb6skjaas6cxq X-HE-Tag: 1766464931-477122 X-HE-Meta: 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 phmtUvZb VVqXgmPd2zTFgTmtJ4GaCpEfPcX4hlrTMr6wpmQj234wg9FzHgt7ZTvXVi6Yyxp2rdu8Ehi8/AqZcX4mxhQnJoiU17uFaMY7BhYKvQnAUUYDNTKX25Llq5Dq+BnSTRjNANxNSgt6bclULPfHbGtmMusvMCha0k8IlIeDbb6lHDjN/7H3u+WqD17kdGSOqWVubBns4 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: To effectively operate with memory cgroups in BPF there is a need to convert css pointers to memcg pointers. A simple container_of cast which is used in the kernel code can't be used in BPF because from the verifier's point of view that's a out-of-bounds memory access. Introduce helper get/put kfuncs which can be used to get a refcounted memcg pointer from the css pointer: - bpf_get_mem_cgroup, - bpf_put_mem_cgroup. bpf_get_mem_cgroup() can take both memcg's css and the corresponding cgroup's "self" css. It allows it to be used with the existing cgroup iterator which iterates over cgroup tree, not memcg tree. Signed-off-by: Roman Gushchin --- mm/Makefile | 3 ++ mm/bpf_memcontrol.c | 88 +++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 91 insertions(+) create mode 100644 mm/bpf_memcontrol.c diff --git a/mm/Makefile b/mm/Makefile index 2d0570a16e5b..bf46fe31dc14 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -106,6 +106,9 @@ obj-$(CONFIG_MEMCG) += memcontrol.o vmpressure.o ifdef CONFIG_SWAP obj-$(CONFIG_MEMCG) += swap_cgroup.o endif +ifdef CONFIG_BPF_SYSCALL +obj-$(CONFIG_MEMCG) += bpf_memcontrol.o +endif obj-$(CONFIG_CGROUP_HUGETLB) += hugetlb_cgroup.o obj-$(CONFIG_GUP_TEST) += gup_test.o obj-$(CONFIG_DMAPOOL_TEST) += dmapool_test.o diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c new file mode 100644 index 000000000000..82eb95de77b7 --- /dev/null +++ b/mm/bpf_memcontrol.c @@ -0,0 +1,88 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Memory Controller-related BPF kfuncs and auxiliary code + * + * Author: Roman Gushchin + */ + +#include +#include + +__bpf_kfunc_start_defs(); + +/** + * bpf_get_mem_cgroup - Get a reference to a memory cgroup + * @css: pointer to the css structure + * + * It's fine to pass a css which belongs to any cgroup controller, + * e.g. unified hierarchy's main css. + * + * Implements KF_ACQUIRE semantics. + * + * Return: A pointer to a mem_cgroup structure after bumping + * the corresponding css's reference counter. + */ +__bpf_kfunc struct mem_cgroup * +bpf_get_mem_cgroup(struct cgroup_subsys_state *css) +{ + struct mem_cgroup *memcg = NULL; + bool rcu_unlock = false; + + if (mem_cgroup_disabled() || !root_mem_cgroup) + return NULL; + + if (root_mem_cgroup->css.ss != css->ss) { + struct cgroup *cgroup = css->cgroup; + int ssid = root_mem_cgroup->css.ss->id; + + rcu_read_lock(); + rcu_unlock = true; + css = rcu_dereference_raw(cgroup->subsys[ssid]); + } + + if (css && css_tryget(css)) + memcg = container_of(css, struct mem_cgroup, css); + + if (rcu_unlock) + rcu_read_unlock(); + + return memcg; +} + +/** + * bpf_put_mem_cgroup - Put a reference to a memory cgroup + * @memcg: memory cgroup to release + * + * Releases a previously acquired memcg reference. + * Implements KF_RELEASE semantics. + */ +__bpf_kfunc void bpf_put_mem_cgroup(struct mem_cgroup *memcg) +{ + css_put(&memcg->css); +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(bpf_memcontrol_kfuncs) +BTF_ID_FLAGS(func, bpf_get_mem_cgroup, KF_ACQUIRE | KF_RET_NULL | KF_RCU) +BTF_ID_FLAGS(func, bpf_put_mem_cgroup, KF_RELEASE) + +BTF_KFUNCS_END(bpf_memcontrol_kfuncs) + +static const struct btf_kfunc_id_set bpf_memcontrol_kfunc_set = { + .owner = THIS_MODULE, + .set = &bpf_memcontrol_kfuncs, +}; + +static int __init bpf_memcontrol_init(void) +{ + int err; + + err = register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, + &bpf_memcontrol_kfunc_set); + if (err) + pr_warn("error while registering bpf memcontrol kfuncs: %d", err); + + return err; +} +late_initcall(bpf_memcontrol_init); -- 2.52.0