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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 48435C48BE5 for ; Thu, 17 Jun 2021 12:13:33 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id A5B9061209 for ; Thu, 17 Jun 2021 12:13:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A5B9061209 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 5575E4B085; Thu, 17 Jun 2021 08:13:32 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 5b+pJExBjUf5; Thu, 17 Jun 2021 08:13:31 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 4AEEB4A523; Thu, 17 Jun 2021 08:13:31 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 051A04A2E5 for ; Thu, 17 Jun 2021 08:13:30 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id lZLq-oXjLTtd for ; Thu, 17 Jun 2021 08:13:28 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id C50064A1A7 for ; Thu, 17 Jun 2021 08:13:28 -0400 (EDT) Received: by mail.kernel.org (Postfix) with ESMTPSA id C580D610EA; Thu, 17 Jun 2021 12:13:24 +0000 (UTC) Date: Thu, 17 Jun 2021 13:13:22 +0100 From: Catalin Marinas To: Steven Price Subject: Re: [PATCH v15 0/7] MTE support for KVM guest Message-ID: <20210617121322.GC6314@arm.com> References: <20210614090525.4338-1-steven.price@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210614090525.4338-1-steven.price@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Mon, Jun 14, 2021 at 10:05:18AM +0100, Steven Price wrote: > I realise there are still open questions[1] around the performance of > this series (the 'big lock', tag_sync_lock, introduced in the first > patch). But there should be no impact on non-MTE workloads and until we > get real MTE-enabled hardware it's hard to know whether there is a need > for something more sophisticated or not. Peter Collingbourne's patch[3] > to clear the tags at page allocation time should hide more of the impact > for non-VM cases. So the remaining concern is around VM startup which > could be effectively serialised through the lock. [...] > [1]: https://lore.kernel.org/r/874ke7z3ng.wl-maz%40kernel.org Start-up, VM resume, migration could be affected by this lock, basically any time you fault a page into the guest. As you said, for now it should be fine as long as the hardware doesn't support MTE or qemu doesn't enable MTE in guests. But the problem won't go away. We have a partial solution with an array of locks to mitigate against this but there's still the question of whether we should actually bother for something that's unlikely to happen in practice: MAP_SHARED memory in guests (ignoring the stage 1 case for now). If MAP_SHARED in guests is not a realistic use-case, we have the vma in user_mem_abort() and if the VM_SHARED flag is set together with MTE enabled for guests, we can reject the mapping. We can discuss the stage 1 case separately from this series. -- Catalin _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm