From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754955AbcEDWlw (ORCPT ); Wed, 4 May 2016 18:41:52 -0400 Received: from mga01.intel.com ([192.55.52.88]:54507 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752330AbcEDWlv (ORCPT ); Wed, 4 May 2016 18:41:51 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,579,1455004800"; d="scan'208";a="968921580" Subject: Re: [PATCH v4 10/10] x86/xsaves: Re-enable XSAVES To: Yu-cheng Yu , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org References: Cc: Andy Lutomirski , Borislav Petkov , Sai Praneeth Prakhya , "Ravi V. Shankar" , Fenghua Yu From: Dave Hansen Message-ID: <572A7AAD.5040201@linux.intel.com> Date: Wed, 4 May 2016 15:41:49 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It's my fault, but you also need to go update fpu__xfeature_set_state() and __raw_xsave_addr() The theoretical problem is that you might ask for a __raw_xsave_addr() of a component which has been compacted out of an XSAVES buffer and thus has no address. We could work around this by doing a memmove() and moving the components "up" after the one we are trying to set in order to make space. But, since we *always* call XSAVES with an instruction mask of -1 and end up with a requested feature bitmap (RFBM) equal to XCR0, I think we can do a shortcut because we'll practically *always* have an xcomp_bv==RFBM==XCR0, which means that all (present) components will always have an address. So, the alternative to doing the memmove() is to add some WARN_ON_FPU() checks to enforce xcomp_bv==RFBM==XCR0 in places where we call XSAVES/XRSTORS and __raw_xsave_addr(), maybe more.