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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 7D09DC64E8A for ; Wed, 2 Dec 2020 12:33:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CB42221FE for ; Wed, 2 Dec 2020 12:33:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726737AbgLBMdV (ORCPT ); Wed, 2 Dec 2020 07:33:21 -0500 Received: from mail.skyhub.de ([5.9.137.197]:50848 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726134AbgLBMdU (ORCPT ); Wed, 2 Dec 2020 07:33:20 -0500 Received: from zn.tnic (p200300ec2f161b00e186258fb055049e.dip0.t-ipconnect.de [IPv6:2003:ec:2f16:1b00:e186:258f:b055:49e]) (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 839061EC0445; Wed, 2 Dec 2020 13:32:39 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1606912359; 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=o/X2Q8TjgxS2AV7FMOJUAyk9P7ykB2huuy5Ud2cBljk=; b=fME5MejkgBN0mNXJWemh6uyBGI0q25TJUz52B4+MjOgCtx/vrQOy0f9Ub8yPrBnpMg8dIl 1BtvFqXRtCl5jfju1qfzn/8xxugE+mK0UXIH4WMg2ulGvxAIS6TwI4OPYiLuQNYyxJFg8+ GLKfO3eez6x6jvEShA/6zBynFK93hw4= Date: Wed, 2 Dec 2020 13:32:35 +0100 From: Borislav Petkov To: Juergen Gross Cc: xen-devel@lists.xenproject.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, peterz@infradead.org, luto@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Deep Shah , "VMware, Inc." , Boris Ostrovsky , Stefano Stabellini Subject: Re: [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call Message-ID: <20201202123235.GD2951@zn.tnic> References: <20201120114630.13552-1-jgross@suse.com> <20201120114630.13552-5-jgross@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20201120114630.13552-5-jgross@suse.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 20, 2020 at 12:46:22PM +0100, Juergen Gross wrote: > @@ -123,12 +115,15 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL) > * Try to use SYSRET instead of IRET if we're returning to > * a completely clean 64-bit userspace context. If we're not, > * go to the slow exit path. > + * In the Xen PV case we must use iret anyway. > */ > - movq RCX(%rsp), %rcx > - movq RIP(%rsp), %r11 > > - cmpq %rcx, %r11 /* SYSRET requires RCX == RIP */ > - jne swapgs_restore_regs_and_return_to_usermode > + ALTERNATIVE __stringify( \ > + movq RCX(%rsp), %rcx; \ > + movq RIP(%rsp), %r11; \ > + cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \ > + jne swapgs_restore_regs_and_return_to_usermode), \ > + "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV Why such a big ALTERNATIVE when you can simply do: /* * Try to use SYSRET instead of IRET if we're returning to * a completely clean 64-bit userspace context. If we're not, * go to the slow exit path. * In the Xen PV case we must use iret anyway. */ ALTERNATIVE "", "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV movq RCX(%rsp), %rcx; movq RIP(%rsp), %r11; cmpq %rcx, %r11; /* SYSRET requires RCX == RIP */ \ jne swapgs_restore_regs_and_return_to_usermode ? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette