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=-5.3 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 CEE47C388F9 for ; Sun, 8 Nov 2020 19:37:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2D24B20773 for ; Sun, 8 Nov 2020 19:37:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="rgcvVJMB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728846AbgKHThD (ORCPT ); Sun, 8 Nov 2020 14:37:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57134 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727570AbgKHThC (ORCPT ); Sun, 8 Nov 2020 14:37:02 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 990FFC0613CF; Sun, 8 Nov 2020 11:37:02 -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=GiLI/WRZqbITTzrhW5xC9hNByZe7/IYN85axmMWjvDw=; b=rgcvVJMBvU4qwDVFPmA5eNJVLk Yns5JPL+qAzPLEWqw7Wm0kBLbJX9Jq6EP2FdLGjI3kmRwtrKunVO8OgEeup1vIkNb2y2tt4u4YIqE 7qr7fyqLvPqn4m5oC1LVNrfjVEdd7YMkXF9P5BtC3dOXGI/piKv49js7phKZmoDqRvW2AjDGStg8B U0y8cqLCP4b0tZMARHjcZwTDgxPaLIbjlwJJBjll4iXpzl551XX85doLY1ChCLdZugzvKT0Nd2a+6 1Ty55sDohCbc6dQcj+8KvteGrLuuvWptSSB+vv2lq8VXZx4xqitFoXUviOWagX0YEuwE///L2hiLj oQPoBslQ==; Received: from 54-240-197-225.amazon.com ([54.240.197.225] helo=u3832b3a9db3152.ant.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kbqUR-0000pW-RN; Sun, 08 Nov 2020 19:36:40 +0000 Message-ID: Subject: Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection From: David Woodhouse To: Thomas Gleixner , Jason Gunthorpe , Dan Williams Cc: "Raj, Ashok" , "Tian, Kevin" , "Jiang, Dave" , Bjorn Helgaas , "vkoul@kernel.org" , "Dey, Megha" , "maz@kernel.org" , "bhelgaas@google.com" , "alex.williamson@redhat.com" , "Pan, Jacob jun" , "Liu, Yi L" , "Lu, Baolu" , "Kumar, Sanjay K" , "Luck, Tony" , "jing.lin@intel.com" , "kwankhede@nvidia.com" , "eric.auger@redhat.com" , "parav@mellanox.com" , "rafael@kernel.org" , "netanelg@mellanox.com" , "shahafs@mellanox.com" , "yan.y.zhao@linux.intel.com" , "pbonzini@redhat.com" , "Ortiz, Samuel" , "Hossain, Mona" , "dmaengine@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-pci@vger.kernel.org" , "kvm@vger.kernel.org" Date: Sun, 08 Nov 2020 19:36:34 +0000 In-Reply-To: <87pn4nk7nn.fsf@nanos.tec.linutronix.de> References: <20201103124351.GM2620339@nvidia.com> <20201104124017.GW2620339@nvidia.com> <20201104135415.GX2620339@nvidia.com> <20201106131415.GT2620339@nvidia.com> <20201106164850.GA85879@otc-nc-03> <20201106175131.GW2620339@nvidia.com> <20201107001207.GA2620339@nvidia.com> <87pn4nk7nn.fsf@nanos.tec.linutronix.de> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-elGCJeSQktRJLFVyLfSc" 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-pci@vger.kernel.org --=-elGCJeSQktRJLFVyLfSc Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2020-11-08 at 19:47 +0100, Thomas Gleixner wrote: > This only works when the guest OS actually knows that it runs in a > VM. If the guest can't figure that out, i.e. via CPUID, this cannot be > solved because from the guest OS view that's the same as running on bare > metal. Obviously on bare metal the Vector domain can and must handle > this. >=20 > So this needs some thought. The problem here is that Intel implemented interrupt remapping in a way which is anathema to structured, ordered IRQ domains. When a guest writes an MSI message (addr/data) to the MSI table of a PCI device which has been assigned to that guest, it *doesn't* properly inherit the MSI composition from a parent irqdomain which knows about the (host-side) IOMMU. What actually happens is the hypervisor *traps* the writes to the device's MSI table, and translates them *then*. In *precisely* the fashion which we're trying to avoid for IMS. Now, you can imagine a world where it wasn't like this, where Remappable Format MSI messages don't exist, and where we let guests write native MSI message to the device without trapping =E2=80=94 and where= the IOMMU then sees the incoming interrupt and has to map the APIC ID to a *virtual* CPU for that guest, based on the PCI source-id of the device. In that world, IMS would work naturally. But that isn't how Intel designed interrupt remapping. They *designed* to have to trap and translate as the message is written to the device. So it does look like we're going to need a hypercall interface to compose an MSI message on behalf of the guest, for IMS to use. In fact PCI devices assigned to a guest could use that too, and then we'd only need to trap-and-remap any attempt to write a Compatibility Format MSI to the device's MSI table, while letting Remappable Format messages get written directly. We'd also need a way for an OS running on bare metal to *know* that it's on bare metal and can just compose MSI messages for itself. Since we do expect bare metal to have an IOMMU, perhaps that is just a feature flag on the IOMMU? That or Intel needs to fix the IOMMU to do proper virtualisation and actually translate "Compatibility Format" MSIs for a guest too. --=-elGCJeSQktRJLFVyLfSc 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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