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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 C72CAC433ED for ; Thu, 20 May 2021 11:55:32 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 34E3761090 for ; Thu, 20 May 2021 11:55:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 34E3761090 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58746 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ljhH1-0003w5-1U for qemu-devel@archiver.kernel.org; Thu, 20 May 2021 07:55:31 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53438) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljhG8-0002m9-N3 for qemu-devel@nongnu.org; Thu, 20 May 2021 07:54:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:53336) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljhG6-0006KD-DX for qemu-devel@nongnu.org; Thu, 20 May 2021 07:54:36 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id DAF0161006; Thu, 20 May 2021 11:54:29 +0000 (UTC) Date: Thu, 20 May 2021 12:54:27 +0100 From: Catalin Marinas To: Steven Price Subject: Re: [PATCH v12 4/8] arm64: kvm: Introduce MTE VM feature Message-ID: <20210520115426.GB12251@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-5-steven.price@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210517123239.8025-5-steven.price@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Received-SPF: pass client-ip=198.145.29.99; envelope-from=cmarinas@kernel.org; helo=mail.kernel.org X-Spam_score_int: -66 X-Spam_score: -6.7 X-Spam_bar: ------ X-Spam_report: (-6.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Peter Maydell , "Dr. David Alan Gilbert" , Andrew Jones , Haibo Xu , Suzuki K Poulose , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , James Morse , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu, Julien Thierry Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, May 17, 2021 at 01:32:35PM +0100, Steven Price wrote: > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index c5d1f3c87dbd..8660f6a03f51 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -822,6 +822,31 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot, > return PAGE_SIZE; > } > > +static int sanitise_mte_tags(struct kvm *kvm, unsigned long size, > + kvm_pfn_t pfn) > +{ > + if (kvm_has_mte(kvm)) { > + /* > + * The page will be mapped in stage 2 as Normal Cacheable, so > + * the VM will be able to see the page's tags and therefore > + * they must be initialised first. If PG_mte_tagged is set, > + * tags have already been initialised. > + */ > + unsigned long i, nr_pages = size >> PAGE_SHIFT; > + struct page *page = pfn_to_online_page(pfn); > + > + if (!page) > + return -EFAULT; IIRC we ended up with pfn_to_online_page() to reject ZONE_DEVICE pages that may be mapped into a guest and we have no idea whether they support MTE. It may be worth adding a comment, otherwise, as Marc said, the page wouldn't disappear. > + > + for (i = 0; i < nr_pages; i++, page++) { > + if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > + mte_clear_page_tags(page_address(page)); We started the page->flags thread and ended up fixing it for the host set_pte_at() as per the first patch: https://lore.kernel.org/r/c3293d47-a5f2-ea4a-6730-f5cae26d8a7e@arm.com Now, can we have a race between the stage 2 kvm_set_spte_gfn() and a stage 1 set_pte_at()? Only the latter takes a lock. Or between two kvm_set_spte_gfn() in different VMs? I think in the above thread we concluded that there's only a problem if the page is shared between multiple VMMs (MAP_SHARED). How realistic is this and what's the workaround? Either way, I think it's worth adding a comment here on the race on page->flags as it looks strange that here it's just a test_and_set_bit() while set_pte_at() uses a spinlock. -- Catalin