Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758883AbcJQXbS (ORCPT ); Mon, 17 Oct 2016 19:31:18 -0400 Received: from mail-vk0-f48.google.com ([209.85.213.48]:33031 "EHLO mail-vk0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753763AbcJQXbJ (ORCPT ); Mon, 17 Oct 2016 19:31:09 -0400 MIME-Version: 1.0 In-Reply-To: <20161017230416.GA18900@test-lenovo> References: <1476734984-13839-1-git-send-email-riel@redhat.com> <1476734984-13839-2-git-send-email-riel@redhat.com> <20161017230416.GA18900@test-lenovo> From: Andy Lutomirski Date: Mon, 17 Oct 2016 16:30:47 -0700 Message-ID: Subject: Re: [PATCH RFC 1/3] fpu/x86: add make_fpregs_active(_newstate) helper functions To: Yu-cheng Yu Cc: Rik van Riel , Dave Hansen , "linux-kernel@vger.kernel.org" , Ingo Molnar , Borislav Petkov , Linus Torvalds , Andrew Lutomirski , dave.hansen@intel.linux.com, Thomas Gleixner , "H. Peter Anvin" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 859 Lines: 21 On Mon, Oct 17, 2016 at 4:04 PM, Yu-cheng Yu wrote: > On Mon, Oct 17, 2016 at 01:57:06PM -0700, Andy Lutomirski wrote: >> Dave and/or Yu-cheng: didn't one of you have some code to allow a user >> xstate buffer to be filled from the copy in kernel memory? If we did >> that, we could avoid this mess entirely. > > In copy_fpstate_to_sigframe() (arch/x86/kernel/fpu/signal.c), the > assumption was we have lazy fpu: > > if (fpregs_active() || we want an #NM exception) > copy_fpregs_to_sigframe(); > else > copy kernel buffer to user buffer; > > But this is not the true anymore. Or do you mean something else? Rik wants to add a different form of FPU laziness, and it would be simpler if we could just always copy from a kernel buffer. Does code to do that exist in the tree? --Andy