From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752175AbaFEQoO (ORCPT ); Thu, 5 Jun 2014 12:44:14 -0400 Received: from terminus.zytor.com ([198.137.202.10]:50439 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751997AbaFEQoM (ORCPT ); Thu, 5 Jun 2014 12:44:12 -0400 Message-ID: <53909E46.4020904@zytor.com> Date: Thu, 05 Jun 2014 09:43:50 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Borislav Petkov CC: Andy Lutomirski , Matt Fleming , "linux-kernel@vger.kernel.org" , Ingo Molnar , Ricardo Neri , "tglx@linutronix.de" , "linux-tip-commits@vger.kernel.org" Subject: Re: [tip:x86/efi] x86/efi: Check for unsafe dealing with FPU state in irq ctxt References: <20140605071805.GA16647@pd.tnic> <20140605090206.GA16642@pd.tnic> <20140605155307.GD16642@pd.tnic> <20140605160842.GE16642@pd.tnic> <20140605161834.GF16642@pd.tnic> <53909B50.50407@zytor.com> <20140605163711.GG16642@pd.tnic> In-Reply-To: <20140605163711.GG16642@pd.tnic> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/05/2014 09:37 AM, Borislav Petkov wrote: > On Thu, Jun 05, 2014 at 09:31:12AM -0700, H. Peter Anvin wrote: >> The bottom line is that we can't call EFI from a context where we can't >> use the FPU. Or specifically, we can't then resume execution. > > Can't we allocate a save-state area, stash the state there and let EFI > scribble over it? When EFI returns, we scribble over it back assuming it > has done the saving/restoring on its own. I'm sorry I don't follow. -hpa