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,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 59110C64E7B for ; Wed, 2 Dec 2020 16:48:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DB4CF2222E for ; Wed, 2 Dec 2020 16:48:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730633AbgLBQsB (ORCPT ); Wed, 2 Dec 2020 11:48:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35832 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728654AbgLBQsB (ORCPT ); Wed, 2 Dec 2020 11:48:01 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D3F44C0613CF; Wed, 2 Dec 2020 08:47:20 -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=K8O1LT7aEdvP8ZF4rdGLyQoWXKiQHxVK9Mp0Dmd3oZc=; b=sOp+rvpCb48IB3smxK0BNaIVaW 9JYopgCKnyzgvzZ9VZX6YAaaH3GDTmb73lN0nIW8N2yTPIfOlfPMl4EPSDHRccloT4cQQ+xRCx9gA xRf7jxACEAsqc5889PbAzVe2lLeBwA8Oz8GMZJtK49shAZaZa4k8GMghti0sWkp+mOY6nqY2c8nWw yOTCQbG7GZCcP3AXJtBBkBcanMqUMVOLCQ8XtrSAOCbTTiDhtTB6N0yYgOkQT4zxDJ3AQphnj8Z5p FB78EVmc4t+QWG7a9F5PfmNIth6VFWtBWFUFVLYC99MnI90DQ/8vBpvXkLZMzYt1bGyCMPhklT9Vs 4dmit+Uw==; Received: from 54-240-197-235.amazon.com ([54.240.197.235] helo=u3832b3a9db3152.ant.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkVHT-0006Pj-FH; Wed, 02 Dec 2020 16:47:03 +0000 Message-ID: <4ad0d157c5c7317a660cd8d65b535d3232f9249d.camel@infradead.org> Subject: Re: [PATCH RFC 10/39] KVM: x86/xen: support upcall vector 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: Wed, 02 Dec 2020 16:47:00 +0000 In-Reply-To: <53baeaa7-0fed-d22c-7767-09ae885d13a0@oracle.com> References: <20190220201609.28290-1-joao.m.martins@oracle.com> <20190220201609.28290-11-joao.m.martins@oracle.com> <71753a370cd6f9dd147427634284073b78679fa6.camel@infradead.org> <53baeaa7-0fed-d22c-7767-09ae885d13a0@oracle.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-MynpSOGfQk2K65aZ7T/y" 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 --=-MynpSOGfQk2K65aZ7T/y Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2020-12-02 at 13:12 +0000, Joao Martins wrote: > On 12/2/20 11:17 AM, David Woodhouse wrote: > > I might be more inclined to go for a model where the kernel handles the > > evtchn_pending/evtchn_mask for us. What would go into the irq routing > > table is { vcpu, port# } which get passed to kvm_xen_evtchn_send(). > >=20 >=20 > But passing port to the routing and handling the sending of events wouldn= 't it lead to > unnecessary handling of event channels which aren't handled by the kernel= , compared to > just injecting caring about the upcall? Well, I'm generally in favour of *not* doing things in the kernel that don't need to be there. But if the kernel is going to short-circuit the IPIs and VIRQs, then it's already going to have to handle the evtchn_pending/evtchn_mask bitmaps, and actually injecting interrupts. Given that it has to have that functionality anyway, it seems saner to let the kernel have full control over it and to just expose 'evtchn_send' to userspace. The alternative is to have userspace trying to play along with the atomic handling of those bitmasks too, and injecting events through KVM_INTERRUPT/KVM_SIGNAL_MSI in parallel to the kernel doing so. That seems like *more* complexity, not less. > I wanted to mention the GSI callback method too, but wasn't enterily sure= if eventfd was > enough. That actually works quite nicely even for userspace irqchip. Forgetting Xen for the moment... my model for userspace I/OAPIC with interrupt remapping is that during normal runtime, the irqfd is assigned and things all work and we can even have IRQ posting for eventfds which came from VFIO.=20 When the IOMMU invalidates an IRQ translation, all it does is *deassign* the irqfd from the KVM IRQ. So the next time that eventfd fires, it's caught in the userspace event loop instead. Userspace can then retranslate through the IOMMU and reassign the irqfd for next time. So, back to Xen. As things stand with just the hypercall+shinfo patches I've already rebased, we have enough to do fully functional Xen hosting. The event channels are slow but it *can* be done entirely in userspace =E2=80=94 handling *all* the hypercalls, and delivering interrupt= s to the guest in whatever mode is required. Event channels are a very important optimisation though. For the VMM API I think we should follow the Xen model, mixing the domain-wide and per-vCPU configuration. It's the best way to faithfully model the behaviour a true Xen guest would experience. So KVM_XEN_ATTR_TYPE_CALLBACK_VIA can be used to set one of =E2=80=A2 HVMIRQ_callback_vector, taking a vector# =E2=80=A2 HVMIRQ_callback_gsi for the in-kernel irqchip, taking a GSI# And *maybe* in a later patch it could also handle =E2=80=A2 HVMIRQ_callback_gsi for split-irqchip, taking an eventfd =E2=80=A2 HVMIRQ_callback_pci_intx, taking an eventfd (or a pair, for EOI?= ) I don't know if the latter two really make sense. After all the argument for handling IPI/VIRQ in kernel kind of falls over if we have to bounce out to userspace anyway. So it *only* makes sense if those eventfds actually end up wired *through* userspace to a KVM IRQFD as I described for the IOMMU stuff. In addition to that per-domain setup, we'd also have a per-vCPU KVM_XEN_ATTR_TYPE_VCPU_CALLBACK_VECTOR which takes {vCPU, vector}. --=-MynpSOGfQk2K65aZ7T/y 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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