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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 854F6C8300A for ; Thu, 30 Apr 2020 10:39:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 57E792137B for ; Thu, 30 Apr 2020 10:39:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588243166; bh=6+7qBBamWTT9w7zClGZROm5AeCOL7MN9qOqe5yevm90=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=UkfjEkAIeUlrzKblw0KVsRNVYYj62g6Zay6s/8cgqn36BxD2NFZ2B6mrXsqrx6NWQ a/Qo2KEKLrS82Sr2Pe2ZGao4qmw3GhM2ggFdMAQ412EiInUFauV7+IljkodlvvvAe5 MfeTMdt+0Tl6tgxpECE3tLBMIaTRKN/QLRzLm8rw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726809AbgD3KjZ (ORCPT ); Thu, 30 Apr 2020 06:39:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:55854 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726427AbgD3KjZ (ORCPT ); Thu, 30 Apr 2020 06:39:25 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 A3CF920838; Thu, 30 Apr 2020 10:39:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588243164; bh=6+7qBBamWTT9w7zClGZROm5AeCOL7MN9qOqe5yevm90=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=j4ZaDYWlFfnjJ0Kk6dtybxWMdijfCyiwyxZsPRioDIEIjW2Pq/Kffjmqjr3+J0Ejl JR4YgwOGru7gDKzTHRc+/mOOsVLTS5ejWCp0tS62mKzaXXuC93LMhd13Rxno4+GTvA qmCLkIDor0yLvS+hxfn7Nw42bPZSZSdBu25gx7Rk= Date: Thu, 30 Apr 2020 11:39:19 +0100 From: Will Deacon To: Srivatsa Vaddagiri Cc: konrad.wilk@oracle.com, mst@redhat.com, jasowang@redhat.com, jan.kiszka@siemens.com, stefano.stabellini@xilinx.com, iommu@lists.linux-foundation.org, virtualization@lists.linux-foundation.org, virtio-dev@lists.oasis-open.org, tsoni@codeaurora.org, pratikp@codeaurora.org, christoffer.dall@arm.com, alex.bennee@linaro.org, linux-kernel@vger.kernel.org Subject: Re: [RFC/PATCH 0/1] virtio_mmio: hypervisor specific interfaces for MMIO Message-ID: <20200430103919.GF19932@willie-the-truck> References: <1588240976-10213-1-git-send-email-vatsa@codeaurora.org> <20200430100821.GC19932@willie-the-truck> <20200430102939.GG5097@quicinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200430102939.GG5097@quicinc.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vatsa, On Thu, Apr 30, 2020 at 03:59:39PM +0530, Srivatsa Vaddagiri wrote: > * Will Deacon [2020-04-30 11:08:22]: > > > > This patch is meant to seek comments. If its considered to be in right > > > direction, will work on making it more complete and send the next version! > > > > What's stopping you from implementing the trapping support in the > > hypervisor? Unlike the other patches you sent out, where the guest memory > > is not accessible to the host, there doesn't seem to be any advantage to > > not having trapping support, or am I missing something here? > > I have had this discussion with hypervisor folks. They seem to be > concerned about complexity of having a VM's fault be handled in another > untrusted VM. They are not keen to add MMIO support. Right, but I'm concerned about forking the implementation from the spec and I'm not keen to add these hooks ;) What does your hook actually do? I'm assuming an HVC? If so, then where the fault is handled seems to be unrelated and whether the guest exit is due to an HVC or a stage-2 fault should be immaterial. In other words, I don't follow why the trapping mechanism necessitates the way in which the fault is handled. Will