From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754594AbcIILO2 (ORCPT ); Fri, 9 Sep 2016 07:14:28 -0400 Received: from terminus.zytor.com ([198.137.202.10]:44132 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753820AbcIILOX (ORCPT ); Fri, 9 Sep 2016 07:14:23 -0400 Date: Fri, 9 Sep 2016 04:14:12 -0700 From: tip-bot for Dave Hansen Message-ID: Cc: linux-kernel@vger.kernel.org, dave@sr71.net, dave.hansen@linux.intel.com, hpa@zytor.com, tglx@linutronix.de, mingo@kernel.org Reply-To: tglx@linutronix.de, mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, dave.hansen@linux.intel.com, dave@sr71.net In-Reply-To: <20160729163023.407672D2@viggo.jf.intel.com> References: <20160729163023.407672D2@viggo.jf.intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:mm/pkeys] x86/pkeys: Allow configuration of init_pkru Git-Commit-ID: 76de993727d22eb29c716abacfae9d9444bb7897 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 76de993727d22eb29c716abacfae9d9444bb7897 Gitweb: http://git.kernel.org/tip/76de993727d22eb29c716abacfae9d9444bb7897 Author: Dave Hansen AuthorDate: Fri, 29 Jul 2016 09:30:23 -0700 Committer: Thomas Gleixner CommitDate: Fri, 9 Sep 2016 13:02:28 +0200 x86/pkeys: Allow configuration of init_pkru As discussed in the previous patch, there is a reliability benefit to allowing an init value for the Protection Keys Rights User register (PKRU) which differs from what the XSAVE hardware provides. But, having PKRU be 0 (its init value) provides some nonzero amount of optimization potential to the hardware. It can, for instance, skip writes to the XSAVE buffer when it knows that PKRU is in its init state. The cost of losing this optimization is approximately 100 cycles per context switch for a workload which lightly using XSAVE state (something not using AVX much). The overhead comes from a combinaation of actually manipulating PKRU and the overhead of pullin in an extra cacheline. This overhead is not huge, but it's also not something that I think we should unconditionally inflict on everyone. So, make it configurable both at boot-time and from debugfs. Changes to the debugfs value affect all processes created after the write to debugfs. Signed-off-by: Dave Hansen Cc: linux-arch@vger.kernel.org Cc: Dave Hansen Cc: mgorman@techsingularity.net Cc: arnd@arndb.de Cc: linux-api@vger.kernel.org Cc: linux-mm@kvack.org Cc: luto@kernel.org Cc: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org Link: http://lkml.kernel.org/r/20160729163023.407672D2@viggo.jf.intel.com Signed-off-by: Thomas Gleixner --- arch/x86/mm/pkeys.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c index ddc5494..f88ce0e 100644 --- a/arch/x86/mm/pkeys.c +++ b/arch/x86/mm/pkeys.c @@ -11,6 +11,7 @@ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for * more details. */ +#include /* debugfs_create_u32() */ #include /* mm_struct, vma, etc... */ #include /* PKEY_* */ #include @@ -159,3 +160,68 @@ void copy_init_pkru_to_fpregs(void) */ write_pkru(init_pkru_value_snapshot); } + +static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + char buf[32]; + unsigned int len; + + len = sprintf(buf, "0x%x\n", init_pkru_value); + return simple_read_from_buffer(user_buf, count, ppos, buf, len); +} + +static ssize_t init_pkru_write_file(struct file *file, + const char __user *user_buf, size_t count, loff_t *ppos) +{ + char buf[32]; + ssize_t len; + u32 new_init_pkru; + + len = min(count, sizeof(buf) - 1); + if (copy_from_user(buf, user_buf, len)) + return -EFAULT; + + /* Make the buffer a valid string that we can not overrun */ + buf[len] = '\0'; + if (kstrtouint(buf, 0, &new_init_pkru)) + return -EINVAL; + + /* + * Don't allow insane settings that will blow the system + * up immediately if someone attempts to disable access + * or writes to pkey 0. + */ + if (new_init_pkru & (PKRU_AD_BIT|PKRU_WD_BIT)) + return -EINVAL; + + WRITE_ONCE(init_pkru_value, new_init_pkru); + return count; +} + +static const struct file_operations fops_init_pkru = { + .read = init_pkru_read_file, + .write = init_pkru_write_file, + .llseek = default_llseek, +}; + +static int __init create_init_pkru_value(void) +{ + debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR, + arch_debugfs_dir, NULL, &fops_init_pkru); + return 0; +} +late_initcall(create_init_pkru_value); + +static __init int setup_init_pkru(char *opt) +{ + u32 new_init_pkru; + + if (kstrtouint(opt, 0, &new_init_pkru)) + return 1; + + WRITE_ONCE(init_pkru_value, new_init_pkru); + + return 1; +} +__setup("init_pkru=", setup_init_pkru);