Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934358AbeAHPxy (ORCPT + 1 other); Mon, 8 Jan 2018 10:53:54 -0500 Received: from bombadil.infradead.org ([65.50.211.133]:54664 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934102AbeAHPxx (ORCPT ); Mon, 8 Jan 2018 10:53:53 -0500 Date: Mon, 8 Jan 2018 16:53:47 +0100 From: Peter Zijlstra To: Tim Chen Cc: Thomas Gleixner , Andy Lutomirski , Linus Torvalds , Greg KH , Dave Hansen , Andrea Arcangeli , Andi Kleen , Arjan Van De Ven , David Woodhouse , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC_CTRL feature Message-ID: <20180108155347.GL32035@hirez.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Fri, Jan 05, 2018 at 06:12:19PM -0800, Tim Chen wrote: > +static ssize_t ibrs_enabled_write(struct file *file, > + const char __user *user_buf, > + size_t count, loff_t *ppos) > +{ > + char buf[32]; > + ssize_t len; > + unsigned int enable; > + > + len = min(count, sizeof(buf) - 1); > + if (copy_from_user(buf, user_buf, len)) > + return -EFAULT; > + > + buf[len] = '\0'; > + if (kstrtouint(buf, 0, &enable)) > + return -EINVAL; > + > + if (enable > IBRS_MAX) > + return -EINVAL; > + > + if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL)) { > + ibrs_enabled = IBRS_DISABLED; > + return -EINVAL; > + } > + > + mutex_lock(&spec_ctrl_mutex); > + > + if (enable == IBRS_DISABLED) { > + /* disable IBRS usage */ > + ibrs_admin_disabled = true; > + dynamic_ibrs = 0; > + spec_ctrl_flush_all_cpus(MSR_IA32_SPEC_CTRL, > + SPEC_CTRL_FEATURE_DISABLE_IBRS); > + > + } else if (enable == IBRS_ENABLED) { > + /* enable IBRS usage in kernel */ > + ibrs_admin_disabled = false; > + dynamic_ibrs = 1; I think you need to do: spec_ctrl_flush_all_cpus(MSR_IA32_SPEC_CTRL, SPEC_CTRL_FEATURE_ENABLE_IBRS); here as well, to force all CPUs into a known state. > + > + } else if (enable == IBRS_ENABLED_USER) { > + /* enable IBRS all the time in both userspace and kernel */ > + ibrs_admin_disabled = false; > + dynamic_ibrs = 0; > + spec_ctrl_flush_all_cpus(MSR_IA32_SPEC_CTRL, > + SPEC_CTRL_FEATURE_ENABLE_IBRS); > + } > + > + ibrs_enabled = enable; > + > + mutex_unlock(&spec_ctrl_mutex); > + return count; > +}