Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752517AbeAFVcv (ORCPT + 1 other); Sat, 6 Jan 2018 16:32:51 -0500 Received: from userp2130.oracle.com ([156.151.31.86]:34434 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751274AbeAFVcu (ORCPT ); Sat, 6 Jan 2018 16:32:50 -0500 Date: Sat, 6 Jan 2018 16:32:27 -0500 From: Konrad Rzeszutek Wilk To: Thomas Gleixner Cc: Dave Hansen , "Van De Ven, Arjan" , Konrad Rzeszutek Wilk , Tim Chen , Andy Lutomirski , Linus Torvalds , Greg KH , Andrea Arcangeli , Andi Kleen , 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: <20180106213227.GJ19213@char.us.oracle.com> References: <20180106144110.GA2592@localhost.localdomain> <742ed1d9-7210-8443-0373-5af74f193ab9@intel.com> <0575AF4FD06DD142AD198903C74E1CC87A56C6FE@ORSMSX103.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.8.3 (2017-05-23) X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8766 signatures=668652 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1801060312 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Sat, Jan 06, 2018 at 08:47:19PM +0100, Thomas Gleixner wrote: > On Sat, 6 Jan 2018, Dave Hansen wrote: > > > On 01/06/2018 09:41 AM, Van De Ven, Arjan wrote: > > >>>> .macro DISABLE_IBRS > > >>>> - ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL > > >>>> + testl $1, dynamic_ibrs > > >>> On every system call we end up hammering on this 'dynamic_ibrs' > > >>> variable. And it looks like it can be flipped via the IPI mechanism. > > >>> > > >>> Would it make sense for this to be per-cpu? > > >> > > >> It's probably better to either just make it __read_mostly or get the > > >> static branches that folks were suggesting actually working. > > > > > > I still wonder if this isn't just better as a boot command line > > > > It's simpler that way. But, ideally, we want to make it runtime > > switchable to match the implementation in the distros. > > Stop this silly argument please. The distros shipped lots of crap which we > dont want to have at all. > > I told you folks yesterday what I want to see and the sysctl thing is the > least on that list and it's not needed for getting the important thing - > the protection - to work. I agree. But this is what customers are told to inspect to see if they are impacted. And if in the future versions this goes away or such - they will freak out and cause needless escalations. > > Can we pretty please do the basics and worry about that sysctl or whatever > people have on their wishlist once the dust settled. > > Thanks, > > tglx >