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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 A971FC63777 for ; Mon, 30 Nov 2020 18:02:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 09BDE206F9 for ; Mon, 30 Nov 2020 18:02:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="TMQrHEWB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387898AbgK3SCU (ORCPT ); Mon, 30 Nov 2020 13:02:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52648 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387817AbgK3SCU (ORCPT ); Mon, 30 Nov 2020 13:02:20 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E2E14C0613CF; Mon, 30 Nov 2020 10:01:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Mime-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=lg1/IRsPmvO9DVTV8smf2kgAGqoFtygDKQ6GjrqRXfM=; b=TMQrHEWBa5qbLermdB3Ap/V4mJ 3cDHfquXS7BZOqAQTA8bYWHgDSFP+t36wEomb72dxyucyK/7kBy2k+ag5W4OwMEc3jdh6iub23lKY oZ2KbCyOsa+Uei6915c1zsFv18eSnIyNlFsytlqPP7T4ulVLnoMmVfJq2DWYYUkaRStN8dm2Ss3XL 1nkLZ03sAge1HemRG2Li2dAJYZJwZFDgLBpYkIXnqFvTzDUUystwdGgFl+wgkFiRXfZBghoW3K1hp Zc/rlO5gmj0JKIMLnc7HieckHotzFNxhg1EYPwFxVGH9VOt7IYpc7/Ryf44A3yozp6p1zGOq30Rr6 Ju5IV8sw==; Received: from 54-240-197-239.amazon.com ([54.240.197.239] helo=freeip.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kjnUP-0007yg-1t; Mon, 30 Nov 2020 18:01:29 +0000 Message-ID: <13bc2ca60ca4e6d74c619e65502889961a08c3ff.camel@infradead.org> Subject: Re: [PATCH RFC 11/39] KVM: x86/xen: evtchn signaling via eventfd From: David Woodhouse To: Joao Martins , Ankur Arora Cc: Boris Ostrovsky , Paolo Bonzini , Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Date: Mon, 30 Nov 2020 18:01:25 +0000 In-Reply-To: <05661003-64f0-a32a-5659-6463d4806ef9@oracle.com> 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> <05661003-64f0-a32a-5659-6463d4806ef9@oracle.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-s5323ca3rhxaqo0/GcDc" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by merlin.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-s5323ca3rhxaqo0/GcDc Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2020-11-30 at 17:15 +0000, Joao Martins wrote: > 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: > > > > >=20 > > > > > One thing I didn't quite do at the time, is the whitelisting of u= nregistered > > > > > ports to userspace. ... > But felt it was still worth having this discussion ... should this be > considered or discarded. I suppose we stick with the later for now. Ack. Duly discarded :) > > > > > Perhaps eventfd could be a way to express this? Like if you regis= ter > > > > > without an eventfd it's offloaded, otherwise it's assigned to use= rspace, > > > > > or if neither it's then returned an error without bothering the V= MM. > > > >=20 > > > > I much prefer the simple model where the *only* event channels that= the > > > > kernel knows about are the ones it's expected to handle. > > > >=20 > > > > For any others, the bypass doesn't kick in, and userspace gets the > > > > KVM_EXIT_HYPERCALL exit. > > > >=20 > > >=20 > > > /me nods > > >=20 > > > I should comment on your other patch but: if we're going to make it g= eneric for > > > the userspace hypercall handling, might as well move hyper-v there to= o. 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 se= parate patch :) > >=20 > > There's a limit to how much consolidation we can do because the ABI is > > different; the args are in different registers. > >=20 >=20 > Yes. It would be optionally enabled of course and VMM would have to adjus= t to the new ABI > -- surely wouldn't want to break current users of KVM_EXIT_HYPERV. True, but that means we'd have to keep KVM_EXIT_HYPERV around anyway, and can't actually *remove* it. The "consolidation" gives us more complexity, not less. > > 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. > >=20 >=20 > I definitely like the KVM_EXIT_HYPERCALL better than a KVM_EXIT_XEN users= pace > exit type ;) >=20 > But I guess you still need to co-relate a type of hypercall (Xen guest ca= p enabled?) to > tell it's Xen or KVM to specially enlighten certain opcodes (EVTCHNOP_sen= d). Sure, but if the VMM doesn't know what kind of guest it's hosting, we have bigger problems... :) --=-s5323ca3rhxaqo0/GcDc Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCECow ggUcMIIEBKADAgECAhEA4rtJSHkq7AnpxKUY8ZlYZjANBgkqhkiG9w0BAQsFADCBlzELMAkGA1UE BhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgG A1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0EgQ2xpZW50IEF1dGhl bnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTkwMTAyMDAwMDAwWhcNMjIwMTAxMjM1 OTU5WjAkMSIwIAYJKoZIhvcNAQkBFhNkd213MkBpbmZyYWRlYWQub3JnMIIBIjANBgkqhkiG9w0B AQEFAAOCAQ8AMIIBCgKCAQEAsv3wObLTCbUA7GJqKj9vHGf+Fa+tpkO+ZRVve9EpNsMsfXhvFpb8 RgL8vD+L133wK6csYoDU7zKiAo92FMUWaY1Hy6HqvVr9oevfTV3xhB5rQO1RHJoAfkvhy+wpjo7Q cXuzkOpibq2YurVStHAiGqAOMGMXhcVGqPuGhcVcVzVUjsvEzAV9Po9K2rpZ52FE4rDkpDK1pBK+ 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