From nobody Mon Feb 9 06:24:26 2026 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 EA1694949E8 for ; Wed, 21 Jan 2026 14:32:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769005982; cv=none; b=j6DE8UAyy0xXIpgiiaeNMIyeJI0y9EzO82p0k5/Gej2LofpeDcIeRhEQ9qjUMaYEazUb7/mLMDSjFmOxNkghVexhzR2fFzR7tbiZ7xp7Pj9WZS/js0yBfJkKN0+6LxGEeFbZjBDcVDORbAb9kkNl2mEkTQOZXRONYHLtpwWpHZE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769005982; c=relaxed/simple; bh=B9SbX4WYbGs76vMLFe+NouI0mAzbHh0eu5BPhCtuhfM=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=Dk0othvX6urB6MR8IiIoI3ioc05Cv6wr5601TeS+dzrvzUEtMGdTigQr5v1mE1T3/iLgtNKM37UW9h/QqE6NkqcRyzzCHluuOuoNMwyJWQlwppJnthefnInGFrDWxVO3zJOPihsjbqANcsM6jC7V/TesZuVTiioiYqzWIJXBbKc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=GuiwRe+v; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="GuiwRe+v" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=UtBtm/u4go1XmuqVciveuo53WUevG8gCdMXQb2Gp7lk=; b=GuiwRe+vyn6ALh48s8CDu/fvu6 1bmw8z/7+oQ0NA1QxXOGqwk3MNezgddWYt8FRlJ2Tkcmmqg0NFbgJtVxFOrAerfMjgawM+xR5TXXo Lx/A4T59V/LcvIDnKYUxEaRN2/OrfzmniNBwopkeWGtlOJUV88SYyFwqjnM5DZJPhOoBYUeo6tqXX YQJpP06YaV3WG9p57XMlLM5A4KtmyJzRmbcUCtFQyp8l4n6Iqxl6sSz4sRadnewAOCdO1cd8eqvOy vQTLJAA8QUDpFa2uOgR02y3qwGJ0HC5DO8Snh9d2c4FCA8gosYsEf5Tb23rSFgKbgXkzK/cEcbSeg aV678JhQ==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1viZGF-0000000GCYH-00rH; Wed, 21 Jan 2026 14:32:47 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id 885403007E1; Wed, 21 Jan 2026 15:32:42 +0100 (CET) Message-ID: <20260121143207.814193010@infradead.org> User-Agent: quilt/0.68 Date: Wed, 21 Jan 2026 15:24:58 +0100 From: Peter Zijlstra To: tglx@linutronix.de, mathieu.desnoyers@efficios.com Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, paulmck@kernel.org, boqun.feng@gmail.com, corbet@lwn.net, prakash.sangappa@oracle.com, vineethr@linux.ibm.com, kprateek.nayak@amd.com, rostedt@goodmis.org, bigeasy@linutronix.de, arnd@arndb.de, rdunlap@infradead.org, rongevarg@gmail.com, longman@redhat.com Subject: [PATCH 1/5] rseq: Allow registering RSEQ with slice extension References: <20260121142457.242071831@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Since glibc cares about the number of syscalls required to initialize a new thread, allow initializing rseq with slice extension on. This avoids having= to do another prctl(). Requested-by: Mathieu Desnoyers Signed-off-by: Peter Zijlstra (Intel) --- include/uapi/linux/rseq.h | 3 ++- kernel/rseq.c | 12 ++++++++++-- 2 files changed, 12 insertions(+), 3 deletions(-) --- a/include/uapi/linux/rseq.h +++ b/include/uapi/linux/rseq.h @@ -19,7 +19,8 @@ enum rseq_cpu_id_state { }; =20 enum rseq_flags { - RSEQ_FLAG_UNREGISTER =3D (1 << 0), + RSEQ_FLAG_UNREGISTER =3D (1 << 0), + RSEQ_FLAG_SLICE_EXT_DEFAULT_ON =3D (1 << 1), }; =20 enum rseq_cs_flags_bit { --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -424,7 +424,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user return 0; } =20 - if (unlikely(flags)) + if (unlikely(flags & ~(RSEQ_FLAG_SLICE_EXT_DEFAULT_ON))) return -EINVAL; =20 if (current->rseq.usrptr) { @@ -459,8 +459,12 @@ SYSCALL_DEFINE4(rseq, struct rseq __user if (!access_ok(rseq, rseq_len)) return -EFAULT; =20 - if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) + if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) { rseqfl |=3D RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE; + if (rseq_slice_extension_enabled() && + (flags & RSEQ_FLAG_SLICE_EXT_DEFAULT_ON)) + rseqfl |=3D RSEQ_CS_FLAG_SLICE_EXT_ENABLED; + } =20 scoped_user_write_access(rseq, efault) { /* @@ -488,6 +492,10 @@ SYSCALL_DEFINE4(rseq, struct rseq __user current->rseq.len =3D rseq_len; current->rseq.sig =3D sig; =20 +#ifdef CONFIG_RSEQ_SLICE_EXTENSION + current->rseq.slice.state.enabled =3D !!(rseqfl & RSEQ_CS_FLAG_SLICE_EXT_= ENABLED); +#endif + /* * If rseq was previously inactive, and has just been * registered, ensure the cpu_id_start and cpu_id fields