From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 0244231355D; Sun, 17 May 2026 21:12:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779052364; cv=none; b=buTEbIsQJJTYpTcH9dWudHkY3+yGomAtrZudo7LPfrZrpwcOZCUP11vy+aOwvhw+XwiJKqT8LeRGma6bNh+Xn9Ks8kDHMwbd6mKw/Q7x9pPwFZ3tgAljJEYhqO4qh3t7f5te+wOMvhGv58Pi/0aHvLpQ6tdgnI8su/vgGGh9chU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779052364; c=relaxed/simple; bh=LHSQ1SGJL53/9Q/iBKU3YD2olZY7RKf5FJ0iXpw1GQA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=k5NlRJm+/wHOi36E6p1yfe2s6wtPMEWWRqW4VjzT+GfE+mitRSCTAvG8S1CKMsqzrE20m5QGwuAj/kNGybxElQXyggMegNdX84I7tdgN+1iLQJthB1w/fw2LDnrkz8sLC1wdgv90tP4yl3OJG+84AoSmvifXVaQdJijw0VaKofE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NnANAk3G; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NnANAk3G" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 80CD3C2BCC6; Sun, 17 May 2026 21:12:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1779052359; bh=LHSQ1SGJL53/9Q/iBKU3YD2olZY7RKf5FJ0iXpw1GQA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NnANAk3G8Dk0DG5c4GgZfuCZMgsvIt2JOV1c83LG8IAsAFIujoM0ARgHCwnaKpLi8 IDkCchIGLmRWKrnHg/fHXqE/0q0/QWAPYSzGFVwNGtF5e0Ha3811HjO6OTdzmVTPwF 1X/RnE7eL5S2rxAm6PHaT2j7FL6GBWlkSu+S+uNyc0jA5+fkblbMLcToOyH6ygBCPx 0jNMdLuZTtjbARsP4NcJG8D8AklOxJ+4Ln3vUY22Vx2baWK/4Vyz1RKKmgpq174d4E wgP7rdlUmDCufQIkqMwpsKyd7yNHxsI5pXeaPLmihhfDZqQgjzqhoADkAWXzC/srgL 0S84ES673/azg== From: Tejun Heo To: David Vernet , Andrea Righi , Changwoo Min , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Kumar Kartikeya Dwivedi Cc: Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Andrew Morton , David Hildenbrand , Mike Rapoport , Emil Tsalapatis , sched-ext@lists.linux.dev, bpf@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tejun Heo Subject: [PATCH 6/8] sched_ext: Require an arena for cid-form schedulers Date: Sun, 17 May 2026 11:12:30 -1000 Message-ID: <20260517211232.1670594-7-tj@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260517211232.1670594-1-tj@kernel.org> References: <20260517211232.1670594-1-tj@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Upcoming patches will let the kernel place arena-resident scratch shared with the BPF program (e.g. per-CPU set_cmask cmask) so the BPF side can dereference it directly via __arena pointers, replacing the current cmask_copy_from_kernel() probe-read loop. That requires each cid-form scheduler to expose its arena to the kernel. Kernel- side accesses are recovered by the per-arena scratch-page mechanism. bpf_scx_reg_cid() walks the struct_ops member progs via bpf_struct_ops_for_each_prog() and reads each prog's arena via bpf_prog_arena(). The verifier enforces one arena per program, so each member prog contributes at most one arena. All non-NULL contributions must match and at least one member prog must use an arena. The map ref is held on scx_sched and dropped on sched destroy. cpu-form schedulers (bpf_scx_reg) are unchanged - no arena requirement. Signed-off-by: Tejun Heo --- kernel/sched/ext.c | 56 ++++++++++++++++++++++++++++++++++++- kernel/sched/ext_internal.h | 8 ++++++ 2 files changed, 63 insertions(+), 1 deletion(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 64f8a096f133..94aab7037329 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -5009,6 +5009,8 @@ static void scx_sched_free_rcu_work(struct work_struct *work) rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL); free_exit_info(sch->exit_info); + if (sch->arena_map) + bpf_map_put(sch->arena_map); kfree(sch); } @@ -6732,6 +6734,7 @@ struct scx_enable_cmd { struct sched_ext_ops_cid *ops_cid; }; bool is_cid_type; + struct bpf_map *arena_map; /* arena ref to transfer to sch */ int ret; }; @@ -6898,6 +6901,15 @@ static struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd, return ERR_PTR(ret); } #endif /* CONFIG_EXT_SUB_SCHED */ + + /* + * Consume the arena_map ref bpf_scx_reg_cid() took. Defer to here so + * earlier failure paths leave cmd->arena_map set and bpf_scx_reg_cid + * drops the ref. After this point, sch owns the ref and any cleanup + * runs through scx_sched_free_rcu_work() which puts it. + */ + sch->arena_map = cmd->arena_map; + cmd->arena_map = NULL; return sch; #ifdef CONFIG_EXT_SUB_SCHED @@ -7884,11 +7896,53 @@ static int bpf_scx_reg(void *kdata, struct bpf_link *link) return scx_enable(&cmd, link); } +struct scx_arena_scan { + struct bpf_map *arena; + int err; +}; + +/* + * The verifier enforces one arena per BPF program, so each struct_ops + * member prog contributes at most one arena via bpf_prog_arena(). + * Require all non-NULL contributions to match. + */ +static int scx_arena_scan_prog(struct bpf_prog *prog, void *data) +{ + struct scx_arena_scan *s = data; + struct bpf_map *arena = bpf_prog_arena(prog); + + if (!arena) + return 0; + if (s->arena && s->arena != arena) { + s->err = -EINVAL; + return 1; + } + s->arena = arena; + return 0; +} + static int bpf_scx_reg_cid(void *kdata, struct bpf_link *link) { struct scx_enable_cmd cmd = { .ops_cid = kdata, .is_cid_type = true }; + struct scx_arena_scan scan = {}; + int ret; - return scx_enable(&cmd, link); + bpf_struct_ops_for_each_prog(kdata, scx_arena_scan_prog, &scan); + if (scan.err) { + pr_err("sched_ext: cid-form scheduler uses multiple arena maps\n"); + return scan.err; + } + if (!scan.arena) { + pr_err("sched_ext: cid-form scheduler must use a BPF arena map\n"); + return -EINVAL; + } + + bpf_map_inc(scan.arena); + cmd.arena_map = scan.arena; + ret = scx_enable(&cmd, link); + if (cmd.arena_map) /* not consumed by scx_alloc_and_add_sched() */ + bpf_map_put(cmd.arena_map); + return ret; } static void bpf_scx_unreg(void *kdata, struct bpf_link *link) diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h index 7258aea94b9f..d40cfd29ddaa 100644 --- a/kernel/sched/ext_internal.h +++ b/kernel/sched/ext_internal.h @@ -1111,6 +1111,14 @@ struct scx_sched { struct sched_ext_ops_cid ops_cid; }; bool is_cid_type; /* true if registered via bpf_sched_ext_ops_cid */ + + /* + * Arena map auto-discovered from member progs at struct_ops attach. + * cid-form schedulers must use exactly one arena across all member + * progs. NULL on cpu-form. + */ + struct bpf_map *arena_map; + DECLARE_BITMAP(has_op, SCX_OPI_END); /* -- 2.54.0