From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from theia.8bytes.org (8bytes.org [81.169.241.247]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3A12471 for ; Wed, 12 May 2021 08:37:40 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id E8C872A5; Wed, 12 May 2021 10:37:37 +0200 (CEST) Date: Wed, 12 May 2021 10:37:34 +0200 From: 'Joerg Roedel' To: David Laight Cc: "x86@kernel.org" , Hyunwook Baek , Joerg Roedel , "stable@vger.kernel.org" , "hpa@zytor.com" , Andy Lutomirski , Dave Hansen , Peter Zijlstra , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Sean Christopherson , Martin Radev , Arvind Sankar , "linux-coco@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "virtualization@lists.linux-foundation.org" Subject: Re: [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user Message-ID: References: <20210512075445.18935-1-joro@8bytes.org> <20210512075445.18935-4-joro@8bytes.org> <0496626f018d4d27a8034a4822170222@AcuMS.aculab.com> X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0496626f018d4d27a8034a4822170222@AcuMS.aculab.com> On Wed, May 12, 2021 at 08:04:33AM +0000, David Laight wrote: > That can't be right at all. > __put/get_user() are only valid on user addresses and will try to > fault in a missing page - so can sleep. Yes, in general these functions can sleep, but not in this context. They are called in atomic context and the page-fault handler will notice that and goes down the __bad_area_nosemaphore() path and only do the fixup. I also thought about adding page_fault_disable()/page_fault_enable() calls, but being in atomic context is enough according to the faulthandler_disabled() implementation. This is exactly what is needed here. All I want to know is whether a fault happened or not, the page-fault handler must not try to fix the fault in any way. If a fault happens it is later fixed up in vc_forward_exception(). > At best this is abused the calls. Yes, but that is only due to the naming of these functions. In this case they do exactly what is needed. Regards, Joerg 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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 08C93C433B4 for ; Wed, 12 May 2021 08:37:45 +0000 (UTC) Received: from smtp4.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4F6CC610F8 for ; Wed, 12 May 2021 08:37:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F6CC610F8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=virtualization-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp4.osuosl.org (Postfix) with ESMTP id D6C7D404B4; Wed, 12 May 2021 08:37:43 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp4.osuosl.org ([127.0.0.1]) by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id JVhnKryWCMkm; Wed, 12 May 2021 08:37:42 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by smtp4.osuosl.org (Postfix) with ESMTP id 36E8740467; Wed, 12 May 2021 08:37:42 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id EB599C000E; Wed, 12 May 2021 08:37:41 +0000 (UTC) Received: from smtp2.osuosl.org (smtp2.osuosl.org [IPv6:2605:bc80:3010::133]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1D5CCC0001 for ; Wed, 12 May 2021 08:37:41 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id F3518402D4 for ; Wed, 12 May 2021 08:37:40 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Ov1jWMHoPSQw for ; Wed, 12 May 2021 08:37:40 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.8.0 Received: from theia.8bytes.org (8bytes.org [IPv6:2a01:238:4383:600:38bc:a715:4b6d:a889]) by smtp2.osuosl.org (Postfix) with ESMTPS id 4BB9140015 for ; Wed, 12 May 2021 08:37:40 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id E8C872A5; Wed, 12 May 2021 10:37:37 +0200 (CEST) Date: Wed, 12 May 2021 10:37:34 +0200 From: 'Joerg Roedel' To: David Laight Subject: Re: [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user Message-ID: References: <20210512075445.18935-1-joro@8bytes.org> <20210512075445.18935-4-joro@8bytes.org> <0496626f018d4d27a8034a4822170222@AcuMS.aculab.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <0496626f018d4d27a8034a4822170222@AcuMS.aculab.com> Cc: "kvm@vger.kernel.org" , Peter Zijlstra , Dave Hansen , "virtualization@lists.linux-foundation.org" , Arvind Sankar , "hpa@zytor.com" , Jiri Slaby , "x86@kernel.org" , David Rientjes , Martin Radev , Tom Lendacky , Joerg Roedel , Kees Cook , Cfir Cohen , Hyunwook Baek , "linux-coco@lists.linux.dev" , Andy Lutomirski , Dan Williams , Juergen Gross , Mike Stunes , Sean Christopherson , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , Masami Hiramatsu , Erdem Aktas X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Wed, May 12, 2021 at 08:04:33AM +0000, David Laight wrote: > That can't be right at all. > __put/get_user() are only valid on user addresses and will try to > fault in a missing page - so can sleep. Yes, in general these functions can sleep, but not in this context. They are called in atomic context and the page-fault handler will notice that and goes down the __bad_area_nosemaphore() path and only do the fixup. I also thought about adding page_fault_disable()/page_fault_enable() calls, but being in atomic context is enough according to the faulthandler_disabled() implementation. This is exactly what is needed here. All I want to know is whether a fault happened or not, the page-fault handler must not try to fix the fault in any way. If a fault happens it is later fixed up in vc_forward_exception(). > At best this is abused the calls. Yes, but that is only due to the naming of these functions. In this case they do exactly what is needed. Regards, Joerg _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization