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=-7.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 00A44C64E7B for ; Mon, 30 Nov 2020 17:16:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 916E620725 for ; Mon, 30 Nov 2020 17:16:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="NNUQ4t84" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729160AbgK3RQi (ORCPT ); Mon, 30 Nov 2020 12:16:38 -0500 Received: from aserp2130.oracle.com ([141.146.126.79]:55198 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725955AbgK3RQi (ORCPT ); Mon, 30 Nov 2020 12:16:38 -0500 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0AUH8sHg139397; Mon, 30 Nov 2020 17:15:39 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2020-01-29; bh=8k0Ick0cipBZUE2FRf/GcIuu2yQCXpVdYugdOUXaAg8=; b=NNUQ4t84Z3haogS/rpq2qdRzegHeNgsUN5hbnMbR0PiIlOIKUd/n1nBALmVYObMvnvtq Rx3b8cqc92jengUVO2eXbQDXBEWb5HY0aPpqfk7cbQn8IvGBUobJje5hu021uqcJUPsq wTAqbc0d5WdxJ2sMkOIuMAzN/dss/E0OsFCtp+9hgLjCyxjTgU7BsJmRfTujFwO11XDU lPKCOwqS2BwoR03hUlMu2maia1aNz+DwGqjglX+Q3SF/bx+Wzjttlq5rwNEX/5XCpmnQ 3IM3X4vgLNpQ32oHJP1vpZC235s3hB8B798+/hCXjmgnfsfr/okFMrFMikNMMsD4vR5i pQ== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by aserp2130.oracle.com with ESMTP id 353c2apc9e-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 30 Nov 2020 17:15:39 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0AUHALVU122738; Mon, 30 Nov 2020 17:15:39 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3030.oracle.com with ESMTP id 35404kuc80-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 30 Nov 2020 17:15:39 +0000 Received: from abhmp0005.oracle.com (abhmp0005.oracle.com [141.146.116.11]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0AUHFabm014424; Mon, 30 Nov 2020 17:15:36 GMT Received: from [10.175.212.254] (/10.175.212.254) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 30 Nov 2020 09:15:36 -0800 Subject: Re: [PATCH RFC 11/39] KVM: x86/xen: evtchn signaling via eventfd To: David Woodhouse , Ankur Arora Cc: Boris Ostrovsky , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190220201609.28290-1-joao.m.martins@oracle.com> <20190220201609.28290-12-joao.m.martins@oracle.com> <874d1fa922cb56238676b90bbeeba930d0706500.camel@infradead.org> <18e854e2a84750c2de2d32384710132b83d84286.camel@infradead.org> <0b9d3901-c10b-effd-6278-6afd1e95b09e@oracle.com> <315ea414c2bf938978f7f2c0598e80fa05b4c07b.camel@infradead.org> From: Joao Martins Message-ID: <05661003-64f0-a32a-5659-6463d4806ef9@oracle.com> Date: Mon, 30 Nov 2020 17:15:31 +0000 MIME-Version: 1.0 In-Reply-To: <315ea414c2bf938978f7f2c0598e80fa05b4c07b.camel@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9821 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=1 bulkscore=0 malwarescore=0 mlxscore=0 mlxlogscore=999 phishscore=0 spamscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011300111 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9821 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=1 lowpriorityscore=0 clxscore=1015 bulkscore=0 mlxlogscore=999 phishscore=0 malwarescore=0 spamscore=0 adultscore=0 mlxscore=0 priorityscore=1501 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2011300111 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/30/20 4:48 PM, David Woodhouse wrote: > On Mon, 2020-11-30 at 15:08 +0000, Joao Martins wrote: >> On 11/30/20 12:55 PM, David Woodhouse wrote: >>> On Mon, 2020-11-30 at 12:17 +0000, Joao Martins wrote: >>>> On 11/30/20 9:41 AM, David Woodhouse wrote: >>>>> On Wed, 2019-02-20 at 20:15 +0000, Joao Martins wrote: >>>> One thing I didn't quite do at the time, is the whitelisting of unregistered >>>> ports to userspace. Right now, it's a blacklist i.e. if it's not handled in >>>> the kernel (IPIs, timer vIRQ, etc) it goes back to userspace. When the only >>>> ones which go to userspace should be explicitly requested as such >>>> and otherwise return -ENOENT in the hypercall. >>> >>> Hm, why would -ENOENT be a fast path which needs to be handled in the >>> kernel? >>> >> >> It's not that it's a fast path. >> >> Like sending an event channel to an unbound vector, now becomes an possible vector to >> worry about in userspace VMM e.g. should that port lookup logic be fragile. >> >> So it's more along the lines of Nack-ing the invalid port earlier to rather go >> to go userspace to invalidate it, provided we do the lookup anyway in the kernel. > > If the port lookup logic is fragile, I *want* it in the sandboxed > userspace VMM and not in the kernel :) > Yes definitely -- I think we are on the same page on that. But it's just that we do the lookup *anyways* to check if the kernel has a given evtchn port registered. That's the lookup I am talking about here, with just an extra bit to tell that's a userspace handled port. > And unless we're going to do *all* of the EVTCHNOP_bind*, EVTCHN_close, > etc. handling in the kernel, doesn't userspace have to have all that > logic for managing the port space anyway? > Indeed. > I think it's better to let userspace own it outright, and use the > kernel bypass purely for the fast paths. The VMM can even implement > IPI/VIRQ support in userspace, then use the kernel bypass if/when it's > available. > True, and it's pretty much how it's implemented today. But felt it was still worth having this discussion ... should this be considered or discarded. I suppose we stick with the later for now. >>>> Perhaps eventfd could be a way to express this? Like if you register >>>> without an eventfd it's offloaded, otherwise it's assigned to userspace, >>>> or if neither it's then returned an error without bothering the VMM. >>> >>> I much prefer the simple model where the *only* event channels that the >>> kernel knows about are the ones it's expected to handle. >>> >>> For any others, the bypass doesn't kick in, and userspace gets the >>> KVM_EXIT_HYPERCALL exit. >>> >> >> /me nods >> >> I should comment on your other patch but: if we're going to make it generic for >> the userspace hypercall handling, might as well move hyper-v there too. In this series, >> I added KVM_EXIT_XEN, much like it exists KVM_EXIT_HYPERV -- but with a generic version >> I wonder if a capability could gate KVM_EXIT_HYPERCALL to handle both guest types, while >> disabling KVM_EXIT_HYPERV. But this is probably subject of its own separate patch :) > > There's a limit to how much consolidation we can do because the ABI is > different; the args are in different registers. > Yes. It would be optionally enabled of course and VMM would have to adjust to the new ABI -- surely wouldn't want to break current users of KVM_EXIT_HYPERV. > I do suspect Hyper-V should have marshalled its arguments into the > existing kvm_run->arch.hypercall and used KVM_EXIT_HYPERCALL but I > don't think it makes sense to change it now since it's a user-facing > ABI. I don't want to follow its lead by inventing *another* gratuitous > exit type for Xen though. > I definitely like the KVM_EXIT_HYPERCALL better than a KVM_EXIT_XEN userspace exit type ;) But I guess you still need to co-relate a type of hypercall (Xen guest cap enabled?) to tell it's Xen or KVM to specially enlighten certain opcodes (EVTCHNOP_send). Joao