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 B1BB9C43381 for ; Tue, 26 Feb 2019 16:38:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8189820C01 for ; Tue, 26 Feb 2019 16:38:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728062AbfBZQi1 (ORCPT ); Tue, 26 Feb 2019 11:38:27 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49988 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727203AbfBZQi1 (ORCPT ); Tue, 26 Feb 2019 11:38:27 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E001D3695F; Tue, 26 Feb 2019 16:38:26 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.31]) by smtp.corp.redhat.com (Postfix) with SMTP id E67B15D6B6; Tue, 26 Feb 2019 16:38:23 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 26 Feb 2019 17:38:25 +0100 (CET) Date: Tue, 26 Feb 2019 17:38:22 +0100 From: Oleg Nesterov To: Sebastian Andrzej Siewior Cc: Dave Hansen , 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: <20190226163821.GC21443@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> <20190121112117.GA32538@redhat.com> <20190205111757.oieqgdcdnctoegav@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190205111757.oieqgdcdnctoegav@linutronix.de> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 26 Feb 2019 16:38:27 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sebastian, Sorry, I just noticed your email... On 02/05, Sebastian Andrzej Siewior wrote: > > On 2019-01-21 12:21:17 [+0100], Oleg Nesterov wrote: > > > 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. > > So I assumed that while SIGUSR1 is handled SIGUSR2 will wait until the > current signal is handled. So no interruption. But then SIGSEGV is > probably the exception which will interrupt SIGUSR1. So we would need a > third one… I guess you do not need my answer, but just in case. SIGSEGV is not an exception. A SIGUSR1 handler can be interrupted by any other signal which is not included in sigaction->sa_mask. Even SIGUSR1 can interrupt the handler if SA_NODEFER was used. > The idea was to save the FPU state in-kernel so we don't have to > revalidate everything because userspace had access to it and could do > things. I understand, but this simply can't work, see above. Oleg.