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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D1193C25B45 for ; Mon, 23 Oct 2023 19:10:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230476AbjJWTKF (ORCPT ); Mon, 23 Oct 2023 15:10:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37414 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229462AbjJWTKD (ORCPT ); Mon, 23 Oct 2023 15:10:03 -0400 Received: from mgamail.intel.com (mgamail.intel.com [192.55.52.115]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D708D94; Mon, 23 Oct 2023 12:10:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1698088201; x=1729624201; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=6FMUuDYUTlK2LKUY1b0PZ+zy98w+sI48pzxcDNADCi0=; b=fAZcs097bdJYP5PZWkn4oYp5f3l4akvhyvN1Zhk4m/9/HQk4nebf7qQp fJSqnist22IDwDkKvrjIp/NI+4aSeQ+WP8LLdYdJAMSzqhALEi1UnGO10 6r1Joxy90vrWpiqdtVYu13g+DDtVqvvEvXZ8wsvr+NPFlZtzmvn7Y5tSh nbM8giiUmBcS8x6A1G7i1INzF+QptL0v6hRA5O08slx5snFiTLLNyWc/O LZJaLQk+EF/VxNU/8U5Dl4QOeJo5TAXTTkJwl3xz/tlfwJQREpoZ6LAOr Pax4nXFY1xjfRR3DiKxYOGx9UGBJ8tY4/Naoc4c96XnkxjisDw/sTrwjG w==; X-IronPort-AV: E=McAfee;i="6600,9927,10872"; a="386718669" X-IronPort-AV: E=Sophos;i="6.03,246,1694761200"; d="scan'208";a="386718669" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Oct 2023 12:10:01 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10872"; a="824055761" X-IronPort-AV: E=Sophos;i="6.03,246,1694761200"; d="scan'208";a="824055761" Received: from qwilliam-mobl.amr.corp.intel.com (HELO desk) ([10.212.150.186]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Oct 2023 12:10:00 -0700 Date: Mon, 23 Oct 2023 12:09:49 -0700 From: Pawan Gupta To: Josh Poimboeuf Cc: Andrew Cooper , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Peter Zijlstra , Andy Lutomirski , Jonathan Corbet , Sean Christopherson , Paolo Bonzini , tony.luck@intel.com, ak@linux.intel.com, tim.c.chen@linux.intel.com, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, Alyssa Milburn , Daniel Sneddon , antonio.gomez.iglesias@linux.intel.com, Alyssa Milburn Subject: Re: [RESEND][PATCH 1/6] x86/bugs: Add asm helpers for executing VERW Message-ID: <20231023190949.2gdrqisype5metpj@desk> References: <20231020-delay-verw-v1-0-cff54096326d@linux.intel.com> <20231020-delay-verw-v1-1-cff54096326d@linux.intel.com> <20231021011859.c2rtc4vl7l2cl4q6@desk> <20231021022134.kbey242xq7n754rg@desk> <20231023180806.udbnt4nx3r2bdyi3@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20231023180806.udbnt4nx3r2bdyi3@treble> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 23, 2023 at 11:08:06AM -0700, Josh Poimboeuf wrote: > On Fri, Oct 20, 2023 at 07:21:34PM -0700, Pawan Gupta wrote: > > On Sat, Oct 21, 2023 at 02:33:47AM +0100, Andrew Cooper wrote: > > > On 21/10/2023 2:18 am, Pawan Gupta wrote: > > > > On Sat, Oct 21, 2023 at 12:55:45AM +0100, Andrew Cooper wrote: > > > >> Also it avoids playing games with hiding data inside an instruction. > > > >> It's a neat trick, but the neater trick is avoid it whenever possible. > > > > Thanks for the pointers. I think verw in 32-bit mode won't be able to > > > > address the operand outside of 4GB range. > > > > > > And?  In a 32bit kernel, what lives outside of a 4G range? > > > > > > > Maybe this is fine or could it > > > > be a problem addressing from e.g. KVM module? > > > > > > RIP-relative addressing is disp32.  Which is the same as it is for > > > direct calls. > > > > > > So if your module is far enough away for VERW to have issues, you've got > > > far more basic problems to solve first. > > > > Sorry, I raised the wrong problem. In 64-bit mode, verww only has 32-bit > > of relative addressing, so memory operand has to be within 4GB of > > callsite. That could be a constraint. > > Even on x86-64, modules are mapped within 4GB of the kernel, so I don't > think that's a concern. You are correct, modules are indeed mapped within 4GB of the kernel. So what Andrew suggested is feasible. Is that your preference?