From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751218AbaETU2H (ORCPT ); Tue, 20 May 2014 16:28:07 -0400 Received: from arkanian.console-pimps.org ([212.110.184.194]:35139 "EHLO arkanian.console-pimps.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750726AbaETU2G (ORCPT ); Tue, 20 May 2014 16:28:06 -0400 Date: Tue, 20 May 2014 21:27:55 +0100 From: Matt Fleming To: "H. Peter Anvin" Cc: Ingo Molnar , linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, Borislav Petkov , "Luck, Tony" Subject: Re: [GIT PULL] EFI changes for v3.16 Message-ID: <20140520202755.GI4798@console-pimps.org> References: <20140503130447.GW26088@console-pimps.org> <20140519105129.GF4798@console-pimps.org> <537A8A03.8060604@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <537A8A03.8060604@zytor.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 19 May, at 03:47:31PM, H. Peter Anvin wrote: > > How on earth does this solve anything? The only thing we add here is a > WARN_ON_ONCE()... but the above text already tells us we have a problem. > > It seems, rather, that we need to figure out how to deal with a pstore > in this case. There are a few possibilities: > > 1. We could keep an XSAVE buffer area around for this particular use. > I am *assuming* we don't let more than one CPU into EFI, because I > cannot for my life imagine that this is safe in typical CPUs. Correct. This is actually prohibited by the spec, so we have a lock to enforce it. > 2. Drop the pstore on the floor if !irq_fpu_usable(). > > 3. Allow the pstore, then die (on the assumption that we're dead > anyway.) Personally, I'd prefer 2, but I'm open to suggestions. -- Matt Fleming, Intel Open Source Technology Center