From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4A796C7113B for ; Mon, 21 Jan 2019 11:21:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 17B2020663 for ; Mon, 21 Jan 2019 11:21:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728171AbfAULVW (ORCPT ); Mon, 21 Jan 2019 06:21:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:32994 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727287AbfAULVV (ORCPT ); Mon, 21 Jan 2019 06:21:21 -0500 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4E30E7F410; Mon, 21 Jan 2019 11:21:21 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.163]) by smtp.corp.redhat.com (Postfix) with SMTP id 968FD6012D; Mon, 21 Jan 2019 11:21:18 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 21 Jan 2019 12:21:21 +0100 (CET) Date: Mon, 21 Jan 2019 12:21:17 +0100 From: Oleg Nesterov To: Dave Hansen Cc: Sebastian Andrzej Siewior , Borislav Petkov , Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, Andy Lutomirski , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , kvm@vger.kernel.org, "Jason A. Donenfeld" , Rik van Riel , Dave Hansen Subject: Re: [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Message-ID: <20190121112117.GA32538@redhat.com> References: <20190109114744.10936-1-bigeasy@linutronix.de> <20190109114744.10936-6-bigeasy@linutronix.de> <20190116193603.GK15409@zn.tnic> <20190116224037.xkfnevzkwrck5dtt@linutronix.de> <20190117122253.GC5023@zn.tnic> <20190118211401.4komqsnvuof7563p@linutronix.de> <33f0e144-1eec-b1a1-8858-58f20d5e477d@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33f0e144-1eec-b1a1-8858-58f20d5e477d@intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Mon, 21 Jan 2019 11:21:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/18, Dave Hansen wrote: > > On 1/18/19 1:14 PM, Sebastian Andrzej Siewior wrote: > > The kernel saves task's FPU registers on user's signal stack before > > entering the signal handler. Can we avoid that and have in-kernel memory > > for that? Does someone rely on the FPU registers from the task in the > > signal handler? > > This is part of our ABI for *sure*. Inspecting that state is how > userspace makes sense of MPX or protection keys faults. We even use > this in selftests/. Yes. And in any case I do not understand the idea to use the second in-kernel struct fpu. A signal handler can be interrupted by another signal, this will need to save/restore the FPU state again. Oleg.