From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756875AbbE2Qrk (ORCPT ); Fri, 29 May 2015 12:47:40 -0400 Received: from www.sr71.net ([198.145.64.142]:54161 "EHLO blackbird.sr71.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756418AbbE2Qr1 (ORCPT ); Fri, 29 May 2015 12:47:27 -0400 Message-ID: <5568981C.7080605@sr71.net> Date: Fri, 29 May 2015 09:47:24 -0700 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Ingo Molnar CC: linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, dave.hansen@linux.intel.com, oleg@redhat.com, bp@alien8.de, riel@redhat.com, sbsiddha@gmail.com, luto@amacapital.net, mingo@redhat.com, hpa@zytor.com, fenghua.yu@intel.com Subject: Re: [PATCH 02/19] x86, fpu: Wrap get_xsave_addr() to make it safer References: <20150527183609.964CC3BA@viggo.jf.intel.com> <20150527183610.56178C96@viggo.jf.intel.com> <20150528084140.GA31719@gmail.com> In-Reply-To: <20150528084140.GA31719@gmail.com> 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 On 05/28/2015 01:41 AM, Ingo Molnar wrote: >> > + union fpregs_state *xstate; >> > + >> > + if (!current->thread.fpu.fpstate_active) >> > + return NULL; >> > + /* >> > + * fpu__save() takes the CPU's xstate registers >> > + * and saves them off to the 'fpu memory buffer. >> > + */ >> > + fpu__save(¤t->thread.fpu); >> > + xstate = ¤t->thread.fpu.state; >> > + >> > + return get_xsave_addr(&xstate->xsave, xsave_state); > Small nit, this would become a lot shorter if you introduced a helper local > variable: > > struct fpu *fpu = ¤t->thread.fpu; > > But more importantly, for a generic get_xsave_field_ptr() API, fpu__save() is not > enough: fpu__save() will only save FPU registers into memory if necessary (i.e. if > the FPU is already in use), and if you call it on a task with no FPU state then it > will still have an !fpu->fpstate_active FPU state after the call, with random, > invalid data in the xsave area. But why does this matter? We just did a !fpu.fpstate_active check, so we can't have a !fpu.fpstate_active before or after the call.