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 F2AF6C27C40 for ; Wed, 22 Nov 2023 23:18:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231354AbjKVXS5 (ORCPT ); Wed, 22 Nov 2023 18:18:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47610 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229453AbjKVXS5 (ORCPT ); Wed, 22 Nov 2023 18:18:57 -0500 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 47370D8 for ; Wed, 22 Nov 2023 15:18:53 -0800 (PST) Date: Wed, 22 Nov 2023 23:18:45 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1700695131; 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: in-reply-to:in-reply-to:references:references; bh=JxXGMR68Ffnug5d1GsuemuN3GA7Qv3hraWikP3Qedyg=; b=EKGjeETg1FstPJI4IUIF9cjjTbqw4SiOzQYBToAG/PRyaM3apZI2VzkUQzsX64VhacLKYU McFbkQwAgzMlNjIHOG6MJ+5w7jqYHy/LCciVJ3Mit2qHGpRdkTGOSOpKVOycUXo7qdZXMC OhzwgUxs+eWT7kYTCw1de2PfeRGitOE= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Sebastian Ene Cc: will@kernel.org, James Morse , Suzuki K Poulose , Zenghui Yu , catalin.marinas@arm.com, mark.rutland@arm.com, akpm@linux-foundation.org, maz@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-team@android.com, vdonnefort@google.com, qperret@google.com, smostafa@google.com Subject: Re: [PATCH v3 00/10] arm64: ptdump: View the second stage page-tables Message-ID: References: <20231115171639.2852644-2-sebastianene@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231115171639.2852644-2-sebastianene@google.com> X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Seb, On Wed, Nov 15, 2023 at 05:16:30PM +0000, Sebastian Ene wrote: > Hi, > > This can be used as a debugging tool for dumping the second stage > page-tables. > > When CONFIG_PTDUMP_STAGE2_DEBUGFS is enabled, ptdump registers > '/sys/debug/kvm//stage2_page_tables' entry with debugfs > upon guest creation. This allows userspace tools (eg. cat) to dump the > stage-2 pagetables by reading the registered file. > > Reading the debugfs file shows stage-2 memory ranges in following format: > > > Under pKVM configuration(kvm-arm.mode=protected) ptdump registers an entry > for the host stage-2 pagetables in the following path: > /sys/debug/kvm/host_stage2_page_tables/ > > The tool interprets the pKVM ownership annotation stored in the invalid > entries and dumps to the console the ownership information. To be able > to access the host stage-2 page-tables from the kernel, a new hypervisor > call was introduced which allows us to snapshot the page-tables in a host > provided buffer. The hypervisor call is hidden behind CONFIG_NVHE_EL2_DEBUG > as this should be used under debugging environment. While I think the value of the feature you're proposing is great, I'm not a fan of the current shape of this series. Reusing note_page() for the stage-2 dump is somewhat convenient, but the series pulls a **massive** amount of KVM details outside of KVM: - Open-coding the whole snapshotting interface with EL2 outside of KVM. This is a complete non-starter for me; the kernel<->EL2 interface needs to be owned by the EL1 portions of KVM. - Building page-table walkers using the KVM pgtable library outside of KVM. - Copying (rather than directly calling) the logic responsible for things like FWB and PGD concatenation. - Hoisting the definition of _software bits_ outside of KVM. I'm less concerned about hardware bits since they have an unambiguous meaning. I think exporting the necessary stuff from ptdump into KVM will lead to a much cleaner implementation. -- Thanks, Oliver