From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759556AbbJ3QzL (ORCPT ); Fri, 30 Oct 2015 12:55:11 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:48333 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751842AbbJ3QzJ (ORCPT ); Fri, 30 Oct 2015 12:55:09 -0400 Message-ID: <1446224098.25261.15.camel@infradead.org> Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff From: David Woodhouse To: "Michael S. Tsirkin" , Andy Lutomirski Cc: Christian Borntraeger , Andy Lutomirski , "linux-kernel@vger.kernel.org" , Joerg Roedel , Cornelia Huck , Sebastian Ott , Paolo Bonzini , Christoph Hellwig , Benjamin Herrenschmidt , KVM , Martin Schwidefsky , linux-s390 , Linux Virtualization Date: Fri, 30 Oct 2015 16:54:58 +0000 In-Reply-To: <20151029104301-mutt-send-email-mst@redhat.com> References: <56307BD1.6010806@de.ibm.com> <1446019787.3405.203.camel@infradead.org> <20151028132331-mutt-send-email-mst@redhat.com> <1446039327.3405.216.camel@infradead.org> <20151028155105-mutt-send-email-mst@redhat.com> <1446041609.3405.228.camel@infradead.org> <20151028161424-mutt-send-email-mst@redhat.com> <1446042754.3405.237.camel@infradead.org> <20151028175136-mutt-send-email-mst@redhat.com> <20151029104301-mutt-send-email-mst@redhat.com> Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-RYrJBLoby1vWtMC0m1T8" X-Mailer: Evolution 3.16.5 (3.16.5-3.fc22) 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 --=-RYrJBLoby1vWtMC0m1T8 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable (Sorry, missed part of this before). On Thu, 2015-10-29 at 11:01 +0200, Michael S. Tsirkin wrote: > Isn't this specified by the hypervisor? I don't think this is a good > way to do this: guest security should be up to guest. And it is. When the guest sees an IOMMU, it can choose to use it, or choose not to (or choose to put it in passthrough mode). But as J=C3=B6rg says, we don't have a way for an individual device driver to *request* passthrough mode or not yet; the choice is made by the core IOMMU code (iommu=3Dpt on the command line) =E2=80=94 or by the platform simply statin= g that a given device isn't *covered* by an IOMMU, if that is indeed the case. In *no* circumstance is it sane for a device driver just to "opt out" of using the correct DMA API function calls, and expect that to *magically* cause the IOMMU to be bypassed. > > Everyone seems to agree that x86's emulated Q35 thing > > is just buggy right now and should be taught to use the existing ACPI > > mechanism for enumerating passthrough devices. >=20 > I'm not sure what ACPI has to do with it. > It's about a way for guest users to specify whether > they want to bypass an IOMMU for a given device. No, it absolutely isn't. You might want that =E2=80=94 and see the discussi= on about DMA_ATTR_IOMMU_BYPASS if you do. But that is *utterly* irrelevant to *this* discussion, in which you seem to be advocating that the virtio drivers should remain buggy by just unilaterally not using the DMA API. > By the way, a bunch of code is missing on the QEMU side > to make this useful: > 1. virtio ignores the iommu > 2. vhost user ignores the iommu > 3. dataplane ignores the iommu > 4. vhost-net ignores the iommu > 5. VFIO ignores the iommu No, those things are not useful for fixing the virtio driver bug under discussion here. All we need to do is make the virtio drivers correctly use the DMA API. They should never have passed review and been accepted into the Linux kernel without that. All we need to do first is make sure that the bug we have in the PowerPC IOMMU code (and potentially ARM and/or SPARC?) is fixed, and that it doesn't attempt to use an IOMMU that doesn't exist. And ensure that the virtualised IOMMU on qemu/x86 isn't lying and claiming that it translates for the virtio devices when it doesn't. There are other things we might want to do =E2=80=94 like fixing the IOMMU = that qemu can emulate, and actually making it work with real assigned devices (currently it's totally hosed because it doesn't handle that case at all). And potentially making the virtualised IOMMU actually *do* translation for virtio devices (as opposed to just admitting correctly that it doesn't). But those aren't strictly relevant here, yet. It's not clear what specific uses of the IOMMU you had in mind in your above list =E2=80=94 could you elucidate? --=20 dwmw2 --=-RYrJBLoby1vWtMC0m1T8 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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--=-RYrJBLoby1vWtMC0m1T8-- From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff Date: Fri, 30 Oct 2015 16:54:58 +0000 Message-ID: <1446224098.25261.15.camel@infradead.org> References: <56307BD1.6010806@de.ibm.com> <1446019787.3405.203.camel@infradead.org> <20151028132331-mutt-send-email-mst@redhat.com> <1446039327.3405.216.camel@infradead.org> <20151028155105-mutt-send-email-mst@redhat.com> <1446041609.3405.228.camel@infradead.org> <20151028161424-mutt-send-email-mst@redhat.com> <1446042754.3405.237.camel@infradead.org> <20151028175136-mutt-send-email-mst@redhat.com> <20151029104301-mutt-send-email-mst@redhat.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1271593645991782149==" Return-path: In-Reply-To: <20151029104301-mutt-send-email-mst@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Archive: List-Post: To: "Michael S. Tsirkin" , Andy Lutomirski Cc: linux-s390 , Joerg Roedel , KVM , Benjamin Herrenschmidt , Sebastian Ott , "linux-kernel@vger.kernel.org" , Linux Virtualization , Christian Borntraeger , Andy Lutomirski , Paolo Bonzini , Christoph Hellwig , Martin Schwidefsky List-ID: --===============1271593645991782149== Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-RYrJBLoby1vWtMC0m1T8" --=-RYrJBLoby1vWtMC0m1T8 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable (Sorry, missed part of this before). On Thu, 2015-10-29 at 11:01 +0200, Michael S. Tsirkin wrote: > Isn't this specified by the hypervisor? I don't think this is a good > way to do this: guest security should be up to guest. And it is. When the guest sees an IOMMU, it can choose to use it, or choose not to (or choose to put it in passthrough mode). But as J=C3=B6rg says, we don't have a way for an individual device driver to *request* passthrough mode or not yet; the choice is made by the core IOMMU code (iommu=3Dpt on the command line) =E2=80=94 or by the platform simply statin= g that a given device isn't *covered* by an IOMMU, if that is indeed the case. In *no* circumstance is it sane for a device driver just to "opt out" of using the correct DMA API function calls, and expect that to *magically* cause the IOMMU to be bypassed. > > Everyone seems to agree that x86's emulated Q35 thing > > is just buggy right now and should be taught to use the existing ACPI > > mechanism for enumerating passthrough devices. >=20 > I'm not sure what ACPI has to do with it. > It's about a way for guest users to specify whether > they want to bypass an IOMMU for a given device. No, it absolutely isn't. You might want that =E2=80=94 and see the discussi= on about DMA_ATTR_IOMMU_BYPASS if you do. But that is *utterly* irrelevant to *this* discussion, in which you seem to be advocating that the virtio drivers should remain buggy by just unilaterally not using the DMA API. > By the way, a bunch of code is missing on the QEMU side > to make this useful: > 1. virtio ignores the iommu > 2. vhost user ignores the iommu > 3. dataplane ignores the iommu > 4. vhost-net ignores the iommu > 5. VFIO ignores the iommu No, those things are not useful for fixing the virtio driver bug under discussion here. All we need to do is make the virtio drivers correctly use the DMA API. They should never have passed review and been accepted into the Linux kernel without that. All we need to do first is make sure that the bug we have in the PowerPC IOMMU code (and potentially ARM and/or SPARC?) is fixed, and that it doesn't attempt to use an IOMMU that doesn't exist. And ensure that the virtualised IOMMU on qemu/x86 isn't lying and claiming that it translates for the virtio devices when it doesn't. There are other things we might want to do =E2=80=94 like fixing the IOMMU = that qemu can emulate, and actually making it work with real assigned devices (currently it's totally hosed because it doesn't handle that case at all). And potentially making the virtualised IOMMU actually *do* translation for virtio devices (as opposed to just admitting correctly that it doesn't). But those aren't strictly relevant here, yet. 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