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=-9.0 required=3.0 tests=BAYES_00,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 93D29C07E95 for ; Tue, 20 Jul 2021 13:16:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D80A610D2 for ; Tue, 20 Jul 2021 13:16:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238405AbhGTMgJ (ORCPT ); Tue, 20 Jul 2021 08:36:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:51918 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238424AbhGTMdY (ORCPT ); Tue, 20 Jul 2021 08:33:24 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5969A610CC; Tue, 20 Jul 2021 13:14:02 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1m5pZQ-00EVoq-8p; Tue, 20 Jul 2021 14:14:00 +0100 Date: Tue, 20 Jul 2021 14:13:59 +0100 Message-ID: <87y2a186w8.wl-maz@kernel.org> From: Marc Zyngier To: Quentin Perret Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, will@kernel.org, dbrazdil@google.com, Srivatsa Vaddagiri , Shanker R Donthineni , James Morse , Suzuki K Poulose , Alexandru Elisei , kernel-team@android.com Subject: Re: [PATCH 03/16] KVM: arm64: Turn kvm_pgtable_stage2_set_owner into kvm_pgtable_stage2_annotate In-Reply-To: References: <20210715163159.1480168-1-maz@kernel.org> <20210715163159.1480168-4-maz@kernel.org> <871r7t9tgi.wl-maz@kernel.org> <87zguh8c4l.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: qperret@google.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, will@kernel.org, dbrazdil@google.com, vatsa@codeaurora.org, sdonthineni@nvidia.com, james.morse@arm.com, suzuki.poulose@arm.com, alexandru.elisei@arm.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 Jul 2021 12:36:21 +0100, Quentin Perret wrote: > > On Tuesday 20 Jul 2021 at 12:20:58 (+0100), Marc Zyngier wrote: > > On Tue, 20 Jul 2021 11:38:17 +0100, > > Quentin Perret wrote: > > > > > > On Tuesday 20 Jul 2021 at 11:21:17 (+0100), Marc Zyngier wrote: > > > > On Tue, 20 Jul 2021 11:09:21 +0100, > > > > Quentin Perret wrote: > > > > > > > > > > On Thursday 15 Jul 2021 at 17:31:46 (+0100), Marc Zyngier wrote: > > > > > > @@ -815,7 +807,7 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size, > > > > > > .arg = &map_data, > > > > > > }; > > > > > > > > > > > > - if (owner_id > KVM_MAX_OWNER_ID) > > > > > > + if (!annotation || (annotation & PTE_VALID)) > > > > > > return -EINVAL; > > > > > > > > > > Why do you consider annotation==0 invalid? The assumption so far has > > > > > been that the owner_id for the host is 0, so annotating a range with 0s > > > > > should be a valid operation -- this will be required when e.g. > > > > > transferring ownership of a page back to the host. > > > > > > > > How do you then distinguish it from an empty entry that doesn't map to > > > > anything at all? > > > > > > You don't, but that's beauty of it :) > > > > > > The host starts with a PGD full of zeroes, which in terms of ownership > > > means that it owns the entire (I)PA space. And it loses ownership of a > > > page only when we explicitly annotate it with an owner id != 0. > > > > Right. But this scheme doesn't apply to the guests, does it? > > Right, the meaning of a NULL PTE in guests will clearly be something > different, but I guess the interpretation of what invalid mappings mean > is up to the caller. > > > Don't we > > need something that is non-null to preserve the table refcounting? > > Sure, but do we care? If the table entry gets zeroed we're then > basically using an 'invalid block' mapping to annotate the entire block > range with '0', whatever that means. For guests it won't mean much, but > for the host that would mean sole ownership of the entire range. I see. You let the refcount drop to 0, unmap the table and let transfer the 0 annotation one level up, covering the whole block. I guess I'll revert back to allowing 0, but I'd like to make sure we don't do that for guests unless we actually tear down the address space (checking for KVM_PGTABLE_S2_IDMAP should work). Thanks, M. -- Without deviation from the norm, progress is not possible.