Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753132AbcD0PPx (ORCPT ); Wed, 27 Apr 2016 11:15:53 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:37154 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752591AbcD0PPw (ORCPT ); Wed, 27 Apr 2016 11:15:52 -0400 Message-ID: <1461770135.118304.152.camel@infradead.org> Subject: Re: [PATCH V2 RFC] fixup! virtio: convert to use DMA api From: David Woodhouse To: "Michael S. Tsirkin" , Joerg Roedel Cc: Kevin Wolf , Wei Liu , Andy Lutomirski , qemu-block@nongnu.org, Christian Borntraeger , Jason Wang , Stefano Stabellini , qemu-devel@nongnu.org, peterx@redhat.com, linux-kernel@vger.kernel.org, Amit Shah , iommu@lists.linux-foundation.org, Stefan Hajnoczi , kvm@vger.kernel.org, cornelia.huck@de.ibm.com, pbonzini@redhat.com, virtualization@lists.linux-foundation.org, Anthony PERARD Date: Wed, 27 Apr 2016 16:15:35 +0100 In-Reply-To: <20160427180007-mutt-send-email-mst@redhat.com> References: <1461245745-6710-1-git-send-email-mst@redhat.com> <20160421135416.GE11775@citrix.com> <1461759501.118304.149.camel@infradead.org> <20160427153345-mutt-send-email-mst@redhat.com> <20160427142331.GH17926@8bytes.org> <20160427172630-mutt-send-email-mst@redhat.com> <20160427145632.GI17926@8bytes.org> <20160427180007-mutt-send-email-mst@redhat.com> Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-MZ8VDRvoXs2XLcG8DcJY" 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 bombadil.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: 8924 Lines: 140 --=-MZ8VDRvoXs2XLcG8DcJY Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2016-04-27 at 18:05 +0300, Michael S. Tsirkin wrote: >=20 > I really don't get it. >=20 > There's exactly one device that works now and needs the work-around and > so that we need to support, and that is virtio. It happens to have > exactly the same issue on all platforms. False. We have other devices which are currently *not* translated by the emulated IOMMU and which aren't going to be in the short term either. We also have other devices (emulated hardware NICs) to which precisely the same "we don't need protection" arguments apply, and which we *could* expose to the guest without an IOMMU translation if we really wanted to. It makes as much sense as exposing virtio without an IOMMU, going forward. > Why would we want to work hard to build platform-specific > solutions to a problem that can be solved in 5 lines of > generic code? Because it's a dirty hack in the *wrong* place. --=20 dwmw2 --=-MZ8VDRvoXs2XLcG8DcJY 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 doa5RY7+N4WRusWZDYW/RRWE6i9EL9qV86CVPYqw22UBOUw4/j/HVGCV6TSB8yE5iEwhk/hUuzRr 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