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=-7.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A0158C11D05 for ; Thu, 20 Feb 2020 14:50:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7274C208CD for ; Thu, 20 Feb 2020 14:50:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Gd03US2p" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728311AbgBTOuw (ORCPT ); Thu, 20 Feb 2020 09:50:52 -0500 Received: from mail-oi1-f193.google.com ([209.85.167.193]:33908 "EHLO mail-oi1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728087AbgBTOuv (ORCPT ); Thu, 20 Feb 2020 09:50:51 -0500 Received: by mail-oi1-f193.google.com with SMTP id l136so27784969oig.1 for ; Thu, 20 Feb 2020 06:50:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:reply-to:references :mime-version:content-disposition:in-reply-to:user-agent; bh=YCUtEJ53m7ECqKK3AgOl0cehXlRW5Bi+qbeZF5u/cGo=; b=Gd03US2pURX3tpufgzIPcsHuU48CBvPuzbG655N2Rz5c8F5EN+JlwQ/u7fwPId6h+x 4avt70bXWtqp5kBm/zeBhactVQPHjBYvvjBQNQHHvh8e1LjTYa/hY7ZnnnHOJaSwBhVN fGz7P6w3RiKO3Ah2aRV3b8idbHoM18Dy/IU9gBB58IBVnT1kuN527PmePh2f+PiRQR49 xIqlYaHSB/0U/XlCNevbLJ5DonSQCqnYTXeLeW7wG86TVQshq7jdvOAnN7zeB40cHas3 pPDL90ukHRvLiGpP2fZstQy40PJhSwSRtfizQp0ZioDoSfzwWOGnGtjVW0F/f8LnsRhZ 9oqQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :reply-to:references:mime-version:content-disposition:in-reply-to :user-agent; bh=YCUtEJ53m7ECqKK3AgOl0cehXlRW5Bi+qbeZF5u/cGo=; b=dXgDVQleqD4tq65as0j74itmACSKRceWuM9L2SbmjyEN0KZOVS59dpUMtNY4KO4619 aZ1A4iKTCu3jJLkN2qOrQ46MtuObcFDfBEFQS1iBd9TKCDs6mm8y2AOwOdHWvBNMllkV z+v95rCZxe3uuuuu4VPhHzp2L6EgR7uqj52QzEsl1B8qqjHBROn4zxF60U1lPLJ+HgAL 3TXHeqd+12dOjI6+khFGTk5lLBYUyUjc6aAuqHmRTwg0uRBNjz44ojPBulvSAYjbO6ak msNbn62DgNgbtsXqQqxBVXUehUCs3877btPC9InVaR76Thh0/CQYBkUHnMXX1vhIwSIT iBLg== X-Gm-Message-State: APjAAAXgs8u/pfrvsOba6ZgleUmKGaHs4qkLi3iWb9M85SePXGhd3moB iAJJwXzQT27Pml0YrfG1/A== X-Google-Smtp-Source: APXvYqz8I33kaCgp3GTwzmzy/RMDIMTxVe9rD7G20HB79+/6QsGE8/hYgj8DFw8sqYbzLba7cziyNg== X-Received: by 2002:a05:6808:18:: with SMTP id u24mr2347495oic.10.1582210250197; Thu, 20 Feb 2020 06:50:50 -0800 (PST) Received: from serve.minyard.net (serve.minyard.net. [2001:470:b8f6:1b::1]) by smtp.gmail.com with ESMTPSA id m2sm1171204oim.13.2020.02.20.06.50.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Feb 2020 06:50:49 -0800 (PST) Received: from minyard.net (unknown [IPv6:2001:470:b8f6:1b:9129:b2b8:445c:a4ff]) by serve.minyard.net (Postfix) with ESMTPSA id 3AEFA18000D; Thu, 20 Feb 2020 14:50:49 +0000 (UTC) Date: Thu, 20 Feb 2020 08:50:48 -0600 From: Corey Minyard To: Marc Zyngier Cc: Will Deacon , Catalin Marinas , linux-arm-kernel@lists.infradead.org, Corey Minyard , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] arm64:kgdb: Fix kernel single-stepping Message-ID: <20200220145048.GH3704@minyard.net> Reply-To: minyard@acm.org References: <20200219152403.3495-1-minyard@acm.org> <1416dca51b52dff349923184f41d48e8@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1416dca51b52dff349923184f41d48e8@kernel.org> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 20, 2020 at 02:21:36PM +0000, Marc Zyngier wrote: > On 2020-02-19 15:24, minyard@acm.org wrote: > > From: Corey Minyard > > [...] > > > After studying the EL0 handling for this, I realized an issue with using > > MDSCR to check if single step is enabled: it can be expensive on a VM. > > So check the task flag first to see if single step is enabled. Then > > check MDSCR if the task flag is set. > > Very tangential remark: I'd really like people *not* to try and optimize > Linux based on the behaviour of a hypervisor. In general, reading a > system register is fast, and the fact that it traps on a given hypervisor > at some point may not be true in the future, nor be a valid assumption > across hypervisors. Normally I would agree, but I based this upon git commit https://github.com/torvalds/linux/commit/2a2830703a2371b47f7b50b1d35cb15dc0e2b717 which seemed to say that it was a significant enough factor to do in the EL0 case. -corey > > M. > -- > Jazz is not dead. It just smells funny...