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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 39A9FC282C3 for ; Tue, 22 Jan 2019 17:00:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0899F20870 for ; Tue, 22 Jan 2019 17:00:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="kuezHi2l" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729517AbfAVRAa (ORCPT ); Tue, 22 Jan 2019 12:00:30 -0500 Received: from mail.skyhub.de ([5.9.137.197]:43126 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728719AbfAVRAa (ORCPT ); Tue, 22 Jan 2019 12:00:30 -0500 Received: from zn.tnic (p200300EC2BCBD90089921F1AF5185B6A.dip0.t-ipconnect.de [IPv6:2003:ec:2bcb:d900:8992:1f1a:f518:5b6a]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 724111EC014A; Tue, 22 Jan 2019 18:00:28 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1548176428; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=/jwaeb43GsSlwJ/wwpkZiDEe2fZXmyil6cWcPR206Qo=; b=kuezHi2lNoV7fM+nb9LtGoWiNVxLVJgE9WYVwwKGHlWuI2+1/26geoPimZ97TSni4nkRlF W5rULu5o6Lj3UrQ/5HBohns3P6pp+0ZUtvop82mq6zi9aZXGn8hIiGtYwAnW21ecrnKwp4 bfepe1EScSOsjBzjtXgfRCJuP5aIsUI= Date: Tue, 22 Jan 2019 18:00:23 +0100 From: Borislav Petkov To: Oleg Nesterov Cc: Dave Hansen , Sebastian Andrzej Siewior , 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 , Michael Matz Subject: Re: [PATCH 05/22] x86/fpu: Remove fpu->initialized usage in copy_fpstate_to_sigframe() Message-ID: <20190122170023.GJ26587@zn.tnic> 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> <20190121112117.GA32538@redhat.com> <20190122134015.GI26587@zn.tnic> <20190122161551.GB9745@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190122161551.GB9745@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 22, 2019 at 05:15:51PM +0100, Oleg Nesterov wrote: > I don't know... tried to google, found nothing. > > the comment in /usr/include/sys/ucontext.h mentions SysV/i386 ABI + historical > reasons, this didn't help. So I'm being told by one of the psABI folks that this is not really written down somewhere explicitly but it is the result from the POSIX and psABI treatise of signal handlers, what they're supposed to do, caller- and callee-saved registers, etc. And FPU registers are volatile, i.e., caller-saved. Which means, the handler itself doesn't save them but the caller, which, doesn't really expect any signals - they are async. So the kernel must do that and slap the FPU regs onto the user stack... Hohumm. Makes sense. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.