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=-9.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 B67CCC433DF for ; Thu, 6 Aug 2020 12:01:14 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 88E6D22D06 for ; Thu, 6 Aug 2020 12:01:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=xen.org header.i=@xen.org header.b="v86h2BDL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 88E6D22D06 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1k3czS-0007YK-PH; Thu, 06 Aug 2020 10:19:14 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1k3czR-0007YF-DH for xen-devel@lists.xenproject.org; Thu, 06 Aug 2020 10:19:13 +0000 X-Inumbo-ID: b1ca73ca-bc6a-4c02-ba21-a6d2383a8217 Received: from mail.xenproject.org (unknown [104.130.215.37]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id b1ca73ca-bc6a-4c02-ba21-a6d2383a8217; Thu, 06 Aug 2020 10:19:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=SmE88vg8iPkyIESyDSppIYWzS5C1Aj/g36wK5TIZsdc=; b=v86h2BDL04C1eUr5+lM5gLvMqi D5rKp0d9mWTfWaGNISqbS+IPwFDMvaCUITsL2ROfOXhM18F9ODF3o9GeqD0j7zXbV9nomteQaQCP2 NV3ptGvwc4cugGwBJcQdjevy/n1iTtLDhMABALzSQhJM3sxw/xFRVjbIVbx2k3hJaiZE=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1k3czH-0007dz-2G; Thu, 06 Aug 2020 10:19:03 +0000 Received: from [54.239.6.186] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1k3czG-0007Jv-MQ; Thu, 06 Aug 2020 10:19:02 +0000 Subject: Re: [RFC PATCH V1 04/12] xen/arm: Introduce arch specific bits for IOREQ/DM features To: Oleksandr References: <1596478888-23030-1-git-send-email-olekstysh@gmail.com> <1596478888-23030-5-git-send-email-olekstysh@gmail.com> <8e8a394c-bd2a-4444-9f4b-e022c59e0f81@xen.org> From: Julien Grall Message-ID: <977d80d8-84b5-00dc-7ade-fab38a6ec84a@xen.org> Date: Thu, 6 Aug 2020 11:19:00 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , Andrew Cooper , Ian Jackson , George Dunlap , Oleksandr Tyshchenko , Julien Grall , Jan Beulich , xen-devel@lists.xenproject.org, Daniel De Graaf , Volodymyr Babchuk Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Hi, On 05/08/2020 16:41, Oleksandr wrote: > > On 05.08.20 12:32, Julien Grall wrote: > > Hi Julien. > >> Hi Stefano, >> >> On 05/08/2020 00:22, Stefano Stabellini wrote: >>> On Mon, 3 Aug 2020, Oleksandr Tyshchenko wrote: >>>> From: Oleksandr Tyshchenko >>>> >>>> This patch makes possible to forward Guest MMIO accesses >>>> to a device emulator on Arm and enables that support for >>>> Arm64. >>>> >>>> Also update XSM code a bit to let DM op be used on Arm. >>>> New arch DM op will be introduced in the follow-up patch. >>>> >>>> Please note, at the moment build on Arm32 is broken >>>> (see cmpxchg usage in hvm_send_buffered_ioreq()) if someone >>> >>> Speaking of buffered_ioreq, if I recall correctly, they were only used >>> for VGA-related things on x86. It looks like it is still true. >>> >>> If so, do we need it on ARM? Note that I don't think we can get rid of >>> it from the interface as it is baked into ioreq, but it might be >>> possible to have a dummy implementation on ARM. Or maybe not: looking at >>> xen/common/hvm/ioreq.c it looks like it would be difficult to >>> disentangle bufioreq stuff from the rest of the code. >> >> We possibly don't need it right now. However, this could possibly be >> used in the future (e.g. virtio notification doorbell). >> >>>> @@ -2275,6 +2282,16 @@ static void check_for_vcpu_work(void) >>>>    */ >>>>   void leave_hypervisor_to_guest(void) >>>>   { >>>> +#ifdef CONFIG_IOREQ_SERVER >>>> +    /* >>>> +     * XXX: Check the return. Shall we call that in >>>> +     * continue_running and context_switch instead? >>>> +     * The benefits would be to avoid calling >>>> +     * handle_hvm_io_completion on every return. >>>> +     */ >>> >>> Yeah, that could be a simple and good optimization >> >> Well, it is not simple as it is sounds :). handle_hvm_io_completion() >> is the function in charge to mark the vCPU as waiting for I/O. So we >> would at least need to split the function. >> >> I wrote this TODO because I wasn't sure about the complexity of >> handle_hvm_io_completion(current). Looking at it again, the main >> complexity is the looping over the IOREQ servers. >> >> I think it would be better to optimize handle_hvm_io_completion() >> rather than trying to hack the context_switch() or continue_running(). >> >> [...] >> >>>> diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h >>>> index 5fdb6e8..5823f11 100644 >>>> --- a/xen/include/asm-arm/p2m.h >>>> +++ b/xen/include/asm-arm/p2m.h >>>> @@ -385,10 +385,11 @@ static inline int set_foreign_p2m_entry(struct >>>> domain *d, unsigned long gfn, >>>>                                           mfn_t mfn) >>>>   { >>>>       /* >>>> -     * NOTE: If this is implemented then proper reference counting of >>>> -     *       foreign entries will need to be implemented. >>>> +     * XXX: handle properly reference. It looks like the page may >>>> not always >>>> +     * belong to d. >>> >>> Just as a reference, and without taking away anything from the comment, >>> I think that QEMU is doing its own internal reference counting for these >>> mappings. >> >> I am not sure how this matters here? We can't really trust the DM to >> do the right thing if it is not running in dom0. >> >> But, IIRC, the problem is some of the pages doesn't belong to do a >> domain, so it is not possible to treat them as foreign mapping (e.g. >> you wouldn't be able to grab a reference). This investigation was done >> a couple of years ago, so this may have changed in recent Xen. >> >> As a side note, I am a bit surprised to see most of my original TODOs >> present in the code. What is the plan to solve them? > The plan is to solve most critical TODOs in current series, and rest in > follow-up series if no objections of course. Any pointers how to solve > them properly would be much appreciated. Unfortunately, now I have a > weak understanding how they should be fixed. AFAICT, there is already some discussion about those 3 major TODOs happening. I would suggest to go through the discussions. We can clarify anything if needed. Cheers, -- Julien Grall