Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752566AbcDRPWQ (ORCPT ); Mon, 18 Apr 2016 11:22:16 -0400 Received: from casper.infradead.org ([85.118.1.10]:53797 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751881AbcDRPWN (ORCPT ); Mon, 18 Apr 2016 11:22:13 -0400 Message-ID: <1460992923.3765.8.camel@infradead.org> Subject: Re: [PATCH RFC] fixup! virtio: convert to use DMA api From: David Woodhouse To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, peterx@redhat.com, cornelia.huck@de.ibm.com, Stefan Hajnoczi , Kevin Wolf , Amit Shah , qemu-block@nongnu.org, Jason Wang , Alex Williamson , Andy Lutomirski , Christian Borntraeger , Wei Liu , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org Date: Mon, 18 Apr 2016 11:22:03 -0400 In-Reply-To: <20160418170534-mutt-send-email-mst@redhat.com> References: <1460979793-6621-1-git-send-email-mst@redhat.com> <1460980717.12793.43.camel@infradead.org> <20160418160731-mutt-send-email-mst@redhat.com> <1460988232.22654.7.camel@infradead.org> <20160418170534-mutt-send-email-mst@redhat.com> Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-Cd7vLFt0wvHwO6N28RYu" X-Mailer: Evolution 3.18.5.2 (3.18.5.2-1.fc23) Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9813 Lines: 161 --=-Cd7vLFt0wvHwO6N28RYu Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2016-04-18 at 17:23 +0300, Michael S. Tsirkin wrote: >=20 > This patch doesn't change DMAR tables, it creates a way for virtio > device to tell guest "I obey what DMAR tables tell you, you can stop > doing hacks". >=20 > And as PPC guys seem adamant that platform tools there are no good for > that purpose, there's another bit that says "ignore what platform tells > you, I'm not a real device - I'm part of hypervisor and I bypass the > IOMMU". ... +/* Request IOMMU passthrough (if available) + * Without VIRTIO_F_IOMMU_PLATFORM: bypass the IOMMU even if enabled. + * With VIRTIO_F_IOMMU_PLATFORM: suggest disabling IOMMU. + */ +#define VIRTIO_F_IOMMU_PASSTHROUGH=C2=A0=C2=A0=C2=A0=C2=A0=C2=A033 + +/* Do not bypass the IOMMU (if configured) */ +#define VIRTIO_F_IOMMU_PLATFORM=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A034 OK... let's see if I can reconcile those descriptions coherently. Setting (only) VIRTIO_F_IOMMU_PASSTHROUGH indicates to the guest that its own operating system's IOMMU code is expected to be broken, and that the virtio driver should eschew the DMA API? And that the guest OS cannot further assign the affected device to any of *its* nested guests? Not that the broken IOMMU code in said guest OS will know the latter, of course. With VIRTIO_F_IOMMU_PLATFORM set, VIRTIO_F_IOMMU_PASSTHROUGH is just a *hint*, suggesting that the guest OS should *request* a passthrough mapping from the IOMMU? Via a driver=E2=86=90=E2=86=92IOMMU API which doesn= 't yet exist in Linux, since we only have 'iommu=3Dpt' on the command line for that? And having *neither* of those bits sets is the status quo, which means that your OS code might well be broken and need you to eschew the DMA API, but maybe not. --=C2=A0 dwmw2 --=-Cd7vLFt0wvHwO6N28RYu Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIISjjCCBicw ggUPoAMCAQICAw3vNzANBgkqhkiG9w0BAQUFADCBjDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0 YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcx ODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENB MB4XDTE1MDUwNTA5NDM0MVoXDTE2MDUwNTA5NTMzNlowQjEcMBoGA1UEAwwTZHdtdzJAaW5mcmFk ZWFkLm9yZzEiMCAGCSqGSIb3DQEJARYTZHdtdzJAaW5mcmFkZWFkLm9yZzCCASIwDQYJKoZIhvcN AQEBBQADggEPADCCAQoCggEBAMkbm9kPbx1j/X4RVyf/pPKSYwelcco69TvnQQbKM8m8xkWjXJI1 jpJ1jMaGUZGFToINMSZi7lZawUozudWbXSKy1SikENSTJHffsdRAIlsp+hR8vWvjsKUry6sEdqPG 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