Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751778AbbHRATb (ORCPT ); Mon, 17 Aug 2015 20:19:31 -0400 Received: from mail-oi0-f51.google.com ([209.85.218.51]:33423 "EHLO mail-oi0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750874AbbHRATa (ORCPT ); Mon, 17 Aug 2015 20:19:30 -0400 MIME-Version: 1.0 In-Reply-To: <3019C0BF-A7B4-4058-8F92-A6104FE41E1D@zytor.com> References: <20150814071500.GA2678@gmail.com> <20150817080143.GA16928@gmail.com> <3019C0BF-A7B4-4058-8F92-A6104FE41E1D@zytor.com> From: Andy Lutomirski Date: Mon, 17 Aug 2015 17:19:10 -0700 Message-ID: Subject: Re: [GIT PULL] x86 fixes To: "H. Peter Anvin" Cc: Ingo Molnar , Linus Torvalds , Juergen Gross , Andy Lutomirski , Linux Kernel Mailing List , Thomas Gleixner , Peter Zijlstra , Brian Gerst , Denys Vlasenko , Andrew Morton 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: 1101 Lines: 20 On Mon, Aug 17, 2015 at 5:06 PM, H. Peter Anvin wrote: > User space does not need to treat for FPU instructions, except for performance reasons, because the kernel emulates the full x87 FPU. So it is localized to the kernel. But user space needs to avoid SSE2 and such, I suspect. In general, I'd be surprised if things work well if we emulate the FPU (and set CR0.em? I haven't checked out Linux's FPU emulation works) if user code sees fancy instruction sets exposed and possibly even OSXSAVE. None of this matters except for testing, since it's very unlikely that any CPU exists that supports XSAVE, XMM, SSE2, etc but uses emulated x87. But if we emulate such a beast, things could break, and I bet that's what Ingo's seeing. (Also, lots of distros target "i686" these days, and that might cause its own set of problems.) --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/