From nobody Wed Sep 10 05:14:44 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 47B5031197B; Mon, 8 Sep 2025 23:00:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757372405; cv=none; b=nBH62RByUQx/C9h5wMh5dcn9i9Ywodvbp19vnWWmbvw82poSG7Sd7r5zAJ52hiV3933pBtXtiG+92cFsy2/USBO3s1IhGi7R17Oz8SqOGMWTR2IKCjPtbzH2hxKa5TDI3ooXBfQrThCDlCBbOAFzdM1iacYzkiNrX4OvhJpcFdU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757372405; c=relaxed/simple; bh=s5+0dXKO96Z6TE/svvTpMCqloqjUT8B7tIiQkcRJzUI=; h=Message-ID:From:To:Cc:Subject:References:MIME-Version: Content-Type:Date; b=SJ0IFq2BYcao6y6z5DJq0IdA6PkDB0D6iSvlHt6ytOd1HGUPH+5flN9LNBUUhBTHpP4BAARSc7PXTvduW5Dd31Q7xpShCbg5NXMP9qZxoIuWeB6CX6hJqrE3Hmf/igFHgpRf4qx82B6R9xuLA4GMUaEo3fc/BqHzVgvbzCl6Wg4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=MB4gZqJ7; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Tws6YMGy; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="MB4gZqJ7"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Tws6YMGy" Message-ID: <20250908225752.872081859@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1757372401; 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: references:references; bh=q2HI1rZu/rTLqfMxXCHeJvZRAnjrUkclL/FW2QBEeDw=; b=MB4gZqJ7AYPIhpNWNvF3rJ1hQzQ1HN7DUUUqB3junfMwk4xbOflZ47ReyCmlvCBXM9IMXj bMCD+ZQyMXQTIU0jtlui0omMJB7W7tdtbZRvsf/pI3Rg71C23hY7K6+wFsM4TAz6TfDzMS JNVwMqBHADA3B6E5LNoybmLrm/AaCVLEde218YrBDBvwhZVpnMY1oDruX1COlE2rwqkxX4 4j8AeKwuFmtpdzspdavrJ1ScSZggEOcDtv8cdVmNY08QcKaAQ3PqQQb0TnsxE/mSSi4IZW yMKooEnaYqOwDSuYzy7X6qKvTvexBqNdvLTQJdnOVvOzMHxzPIGu/Z8nu37lnw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1757372401; 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: references:references; bh=q2HI1rZu/rTLqfMxXCHeJvZRAnjrUkclL/FW2QBEeDw=; b=Tws6YMGycBqrhvXHfDKm8QmAY1c7fASt6l/C2FD1efOFQOdRaFO2ddBN9Bulvj2KKKrTRV 3NsPgxgGnaE7acCQ== From: Thomas Gleixner To: LKML Cc: Mathieu Desnoyers , Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , Peter Zilstra , Jonathan Corbet , Prakash Sangappa , Madadi Vineeth Reddy , K Prateek Nayak , Steven Rostedt , Sebastian Andrzej Siewior , Arnd Bergmann , linux-arch@vger.kernel.org Subject: [patch 05/12] rseq: Add prctl() to enable time slice extensions References: <20250908225709.144709889@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Tue, 9 Sep 2025 00:59:59 +0200 (CEST) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Implement a prctl() so that tasks can enable the time slice extension mechanism. This fails, when time slice extensions are disabled at compile time or on the kernel command line and when no rseq pointer is registered in the kernel. That allows to implement a single trivial check in the exit to user mode hotpath, to decide whether the whole mechanism needs to be invoked. Signed-off-by: Thomas Gleixner Cc: Mathieu Desnoyers Cc: Peter Zijlstra Cc: "Paul E. McKenney" Cc: Boqun Feng --- include/linux/rseq.h | 9 +++++++ include/uapi/linux/prctl.h | 10 ++++++++ kernel/rseq.c | 52 ++++++++++++++++++++++++++++++++++++++++= +++++ kernel/sys.c | 6 +++++ 4 files changed, 77 insertions(+) --- a/include/linux/rseq.h +++ b/include/linux/rseq.h @@ -190,4 +190,13 @@ void rseq_syscall(struct pt_regs *regs); static inline void rseq_syscall(struct pt_regs *regs) { } #endif /* !CONFIG_DEBUG_RSEQ */ =20 +#ifdef CONFIG_RSEQ_SLICE_EXTENSION +int rseq_slice_extension_prctl(unsigned long arg2, unsigned long arg3); +#else /* CONFIG_RSEQ_SLICE_EXTENSION */ +static inline int rseq_slice_extension_prctl(unsigned long arg2, unsigned = long arg3) +{ + return -EINVAL; +} +#endif /* !CONFIG_RSEQ_SLICE_EXTENSION */ + #endif /* _LINUX_RSEQ_H */ --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -376,4 +376,14 @@ struct prctl_mm_map { # define PR_FUTEX_HASH_SET_SLOTS 1 # define PR_FUTEX_HASH_GET_SLOTS 2 =20 +/* RSEQ time slice extensions */ +#define PR_RSEQ_SLICE_EXTENSION 79 +# define PR_RSEQ_SLICE_EXTENSION_GET 1 +# define PR_RSEQ_SLICE_EXTENSION_SET 2 +/* + * Bits for RSEQ_SLICE_EXTENSION_GET/SET + * PR_RSEQ_SLICE_EXT_ENABLE: Enable + */ +# define PR_RSEQ_SLICE_EXT_ENABLE 0x01 + #endif /* _LINUX_PRCTL_H */ --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -71,6 +71,7 @@ #define RSEQ_BUILD_SLOW_PATH =20 #include +#include #include #include #include @@ -490,6 +491,57 @@ SYSCALL_DEFINE4(rseq, struct rseq __user #ifdef CONFIG_RSEQ_SLICE_EXTENSION DEFINE_STATIC_KEY_TRUE(rseq_slice_extension_key); =20 +int rseq_slice_extension_prctl(unsigned long arg2, unsigned long arg3) +{ + switch (arg2) { + case PR_RSEQ_SLICE_EXTENSION_GET: + if (arg3) + return -EINVAL; + return current->rseq.slice.state.enabled ? PR_RSEQ_SLICE_EXT_ENABLE : 0; + + case PR_RSEQ_SLICE_EXTENSION_SET: { + u32 rflags, valid =3D RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE; + bool enable =3D !!(arg3 & PR_RSEQ_SLICE_EXT_ENABLE); + + if (arg3 & ~PR_RSEQ_SLICE_EXT_ENABLE) + return -EINVAL; + if (!rseq_slice_extension_enabled()) + return -ENOTSUPP; + if (!current->rseq.usrptr) + return -ENXIO; + + /* No change? */ + if (enable =3D=3D !!current->rseq.slice.state.enabled) + return 0; + + if (get_user(rflags, ¤t->rseq.usrptr->flags)) + goto die; + + if (current->rseq.slice.state.enabled) + valid |=3D RSEQ_CS_FLAG_SLICE_EXT_ENABLED; + + if ((rflags & valid) !=3D valid) + goto die; + + rflags &=3D ~RSEQ_CS_FLAG_SLICE_EXT_ENABLED; + rflags |=3D RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE; + if (enable) + rflags |=3D RSEQ_CS_FLAG_SLICE_EXT_ENABLED; + + if (put_user(rflags, ¤t->rseq.usrptr->flags)) + goto die; + + current->rseq.slice.state.enabled =3D enable; + return 0; + } + default: + return -EINVAL; + } +die: + force_sig(SIGSEGV); + return -EFAULT; +} + static int __init rseq_slice_cmdline(char *str) { bool on; --- a/kernel/sys.c +++ b/kernel/sys.c @@ -53,6 +53,7 @@ #include #include #include +#include =20 #include #include @@ -2805,6 +2806,11 @@ SYSCALL_DEFINE5(prctl, int, option, unsi case PR_FUTEX_HASH: error =3D futex_hash_prctl(arg2, arg3, arg4); break; + case PR_RSEQ_SLICE_EXTENSION: + if (arg4 || arg5) + return -EINVAL; + error =3D rseq_slice_extension_prctl(arg2, arg3); + break; default: trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5); error =3D -EINVAL;