Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751797AbbKHMAr (ORCPT ); Sun, 8 Nov 2015 07:00:47 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:47523 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750887AbbKHMAp (ORCPT ); Sun, 8 Nov 2015 07:00:45 -0500 Message-ID: <1446984033.81031.9.camel@infradead.org> Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff From: David Woodhouse To: "Michael S. Tsirkin" Cc: Andy Lutomirski , 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: Sun, 08 Nov 2015 12:00:33 +0000 In-Reply-To: <20151108120627-mutt-send-email-mst@redhat.com> References: <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> <1446135536.3405.279.camel@infradead.org> <20151108120627-mutt-send-email-mst@redhat.com> Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-sfIFhvCLM1NIM5uxtI47" X-Mailer: Evolution 3.18.1 (3.18.1-1.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: 11032 Lines: 187 --=-sfIFhvCLM1NIM5uxtI47 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2015-11-08 at 12:37 +0200, Michael S. Tsirkin wrote: > On Thu, Oct 29, 2015 at 05:18:56PM +0100, David Woodhouse wrote: > > On Thu, 2015-10-29 at 11:01 +0200, Michael S. Tsirkin wrote: > > >=20 > > > But you trust your hypervisor (you have no choice anyway), > > > and you don't want the overhead of tweaking IOMMU > > > on data path for virtio. Thus iommu=3Don is out too. > >=20 > > That's not at all special for virtio or guest VMs. Even with real > > hardware, we might want performance from *some* devices, and security > > from others. See the DMA_ATTR_IOMMU_BYPASS which is currently being > > discussed. >=20 > Right. So let's wait for that discussion to play out? That discussion is purely about a requested optimisation. This one is about correctness. > > But of course the easy answer in *your* case it just to ask the > > hypervisor not to put the virtio devices behind an IOMMU at all. Which > > we were planning to remain the default behaviour. >=20 > One can't do this for x86 ATM, can one? The converse is true, in fact =E2=80=94 currently, there's no way to tell= =C2=A0 qemu-system-x86 that you *do* want it to put the virtio devices behind the emulated IOMMU, as it has no support for that. Which is a bit sad really, since the DMAR table that qemu advertises to the guest does *tell* the guest that the virtio devices are behind the emulated IOMMU. In the short term, we'll be fixing the DMAR table, and still not actually making it possible to put the virtio devices behind the emulated IOMMU. In the fullness of time, however, we *will* be fixing the qemu IOMMU code so that it can translate for virtio devices =E2=80=94 and for assigned physical devices, which I believe are also broken at the moment when qemu emulates an IOMMU. > > In all cases, the DMA API shall do the right thing. >=20 > I have no problem with that. For example, can we teach > the DMA API on intel x86 to use PT for virtio by default? > That would allow merging Andy's patches with > full compatibility with old guests and hosts. A quirk so that we *notice* the bug in the existing qemu DMAR table, and disbelieve what it says about the virtio devices? Alternatively, we could just recognise that the emulated IOMMU support in qemu is an experimental feature and doesn't work right, yet. Are people really using it in anger? If we do want to do a quirk, then we should make it get it right for assigned devices too. To start with, do you want to try to express the criteria for "the DMAR table lies and device is actually untranslated" in a form of prose which could reasonably be translated into code? --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-sfIFhvCLM1NIM5uxtI47 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 FZm1MJMR7mCS7BCR8Lr5jFY61lWpBiXNXIxLZCvDc26KR5L5tYX43iUVO3fzES1GRVoYnxxk2tmz fcsZG5vK+Trc9L8OZJfkYrEHH3+Iw41MQ0w/djVtYr1+HYldx0QmYXAtnhIj+UMCAwEAAaOCAtkw ggLVMAkGA1UdEwQCMAAwCwYDVR0PBAQDAgSwMB0GA1UdJQQWMBQGCCsGAQUFBwMCBggrBgEFBQcD BDAdBgNVHQ4EFgQUszC96C3w5/2+d+atSr0IpT26YI4wHwYDVR0jBBgwFoAUU3Ltkpzg2ssBXHx+ ljVO8tS4UYIwHgYDVR0RBBcwFYETZHdtdzJAaW5mcmFkZWFkLm9yZzCCAUwGA1UdIASCAUMwggE/ MIIBOwYLKwYBBAGBtTcBAgMwggEqMC4GCCsGAQUFBwIBFiJodHRwOi8vd3d3LnN0YXJ0c3NsLmNv bS9wb2xpY3kucGRmMIH3BggrBgEFBQcCAjCB6jAnFiBTdGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1 dGhvcml0eTADAgEBGoG+VGhpcyBjZXJ0aWZpY2F0ZSB3YXMgaXNzdWVkIGFjY29yZGluZyB0byB0 aGUgQ2xhc3MgMSBWYWxpZGF0aW9uIHJlcXVpcmVtZW50cyBvZiB0aGUgU3RhcnRDb20gQ0EgcG9s aWN5LCByZWxpYW5jZSBvbmx5IGZvciB0aGUgaW50ZW5kZWQgcHVycG9zZSBpbiBjb21wbGlhbmNl IG9mIHRoZSByZWx5aW5nIHBhcnR5IG9ibGlnYXRpb25zLjA2BgNVHR8ELzAtMCugKaAnhiVodHRw Oi8vY3JsLnN0YXJ0c3NsLmNvbS9jcnR1MS1jcmwuY3JsMIGOBggrBgEFBQcBAQSBgTB/MDkGCCsG AQUFBzABhi1odHRwOi8vb2NzcC5zdGFydHNzbC5jb20vc3ViL2NsYXNzMS9jbGllbnQvY2EwQgYI KwYBBQUHMAKGNmh0dHA6Ly9haWEuc3RhcnRzc2wuY29tL2NlcnRzL3N1Yi5jbGFzczEuY2xpZW50 LmNhLmNydDAjBgNVHRIEHDAahhhodHRwOi8vd3d3LnN0YXJ0c3NsLmNvbS8wDQYJKoZIhvcNAQEF BQADggEBAHMQmxHHodpS85X8HRyxhvfkys7r+taCNOaNU9cxQu/cZ/6k5nS2qGNMzZ6jb7ueY/V7 7p+4DW/9ZWODDTf4Fz00mh5SSVc20Bz7t+hhxwHd62PZgENh5i76Qq2tw48U8AsYo5damHby1epf neZafLpUkLLO7AGBJIiRVTevdvyXQ0qnixOmKMWyvrhSNGuVIKVdeqLP+102Dwf+dpFyw+j1hz28 jEEKpHa+NR1b2kXuSPi/rMGhexwlJOh4tK8KQ6Ryr0rIN//NSbOgbyYZrzc/ZUWX9V5OA84ChFb2 vkFl0OcYrttp/rhDBLITwffPxSZeoBh9H7zYzkbCXKL3BUIwggYnMIIFD6ADAgECAgMN7zcwDQYJ KoZIhvcNAQEFBQAwgYwxCzAJBgNVBAYTAklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSswKQYD VQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0ZSBTaWduaW5nMTgwNgYDVQQDEy9TdGFydENv bSBDbGFzcyAxIFByaW1hcnkgSW50ZXJtZWRpYXRlIENsaWVudCBDQTAeFw0xNTA1MDUwOTQzNDFa Fw0xNjA1MDUwOTUzMzZaMEIxHDAaBgNVBAMME2R3bXcyQGluZnJhZGVhZC5vcmcxIjAgBgkqhkiG 9w0BCQEWE2R3bXcyQGluZnJhZGVhZC5vcmcwggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIB AQDJG5vZD28dY/1+EVcn/6TykmMHpXHKOvU750EGyjPJvMZFo1ySNY6SdYzGhlGRhU6CDTEmYu5W WsFKM7nVm10istUopBDUkyR337HUQCJbKfoUfL1r47ClK8urBHajxnaGuUWO/jeFkbrFmQ2Fv0UV hOovRC/alfOglT2KsNtlATlMOP4/x1Rglek0gfMhOYhMIZP4VLs0axWZtTCTEe5gkuwQkfC6+YxW OtZVqQYlzVyMS2Qrw3NuikeS+bWF+N4lFTt38xEtRkVaGJ8cZNrZs33LGRubyvk63PS/DmSX5GKx Bx9/iMONTENMP3Y1bWK9fh2JXcdEJmFwLZ4SI/lDAgMBAAGjggLZMIIC1TAJBgNVHRMEAjAAMAsG A1UdDwQEAwIEsDAdBgNVHSUEFjAUBggrBgEFBQcDAgYIKwYBBQUHAwQwHQYDVR0OBBYEFLMwvegt 8Of9vnfmrUq9CKU9umCOMB8GA1UdIwQYMBaAFFNy7ZKc4NrLAVx8fpY1TvLUuFGCMB4GA1UdEQQX MBWBE2R3bXcyQGluZnJhZGVhZC5vcmcwggFMBgNVHSAEggFDMIIBPzCCATsGCysGAQQBgbU3AQID MIIBKjAuBggrBgEFBQcCARYiaHR0cDovL3d3dy5zdGFydHNzbC5jb20vcG9saWN5LnBkZjCB9wYI KwYBBQUHAgIwgeowJxYgU3RhcnRDb20gQ2VydGlmaWNhdGlvbiBBdXRob3JpdHkwAwIBARqBvlRo aXMgY2VydGlmaWNhdGUgd2FzIGlzc3VlZCBhY2NvcmRpbmcgdG8gdGhlIENsYXNzIDEgVmFsaWRh dGlvbiByZXF1aXJlbWVudHMgb2YgdGhlIFN0YXJ0Q29tIENBIHBvbGljeSwgcmVsaWFuY2Ugb25s eSBmb3IgdGhlIGludGVuZGVkIHB1cnBvc2UgaW4gY29tcGxpYW5jZSBvZiB0aGUgcmVseWluZyBw YXJ0eSBvYmxpZ2F0aW9ucy4wNgYDVR0fBC8wLTAroCmgJ4YlaHR0cDovL2NybC5zdGFydHNzbC5j b20vY3J0dTEtY3JsLmNybDCBjgYIKwYBBQUHAQEEgYEwfzA5BggrBgEFBQcwAYYtaHR0cDovL29j c3Auc3RhcnRzc2wuY29tL3N1Yi9jbGFzczEvY2xpZW50L2NhMEIGCCsGAQUFBzAChjZodHRwOi8v YWlhLnN0YXJ0c3NsLmNvbS9jZXJ0cy9zdWIuY2xhc3MxLmNsaWVudC5jYS5jcnQwIwYDVR0SBBww GoYYaHR0cDovL3d3dy5zdGFydHNzbC5jb20vMA0GCSqGSIb3DQEBBQUAA4IBAQBzEJsRx6HaUvOV /B0csYb35MrO6/rWgjTmjVPXMULv3Gf+pOZ0tqhjTM2eo2+7nmP1e+6fuA1v/WVjgw03+Bc9NJoe UklXNtAc+7foYccB3etj2YBDYeYu+kKtrcOPFPALGKOXWph28tXqX53mWny6VJCyzuwBgSSIkVU3 r3b8l0NKp4sTpijFsr64UjRrlSClXXqiz/tdNg8H/naRcsPo9Yc9vIxBCqR2vjUdW9pF7kj4v6zB oXscJSToeLSvCkOkcq9KyDf/zUmzoG8mGa83P2VFl/VeTgPOAoRW9r5BZdDnGK7baf64QwSyE8H3 z8UmXqAYfR+82M5Gwlyi9wVCMIIGNDCCBBygAwIBAgIBHjANBgkqhkiG9w0BAQUFADB9MQswCQYD VQQGEwJJTDEWMBQGA1UEChMNU3RhcnRDb20gTHRkLjErMCkGA1UECxMiU2VjdXJlIERpZ2l0YWwg Q2VydGlmaWNhdGUgU2lnbmluZzEpMCcGA1UEAxMgU3RhcnRDb20gQ2VydGlmaWNhdGlvbiBBdXRo b3JpdHkwHhcNMDcxMDI0MjEwMTU1WhcNMTcxMDI0MjEwMTU1WjCBjDELMAkGA1UEBhMCSUwxFjAU BgNVBAoTDVN0YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRl IFNpZ25pbmcxODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUg Q2xpZW50IENBMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAxwmDzM4t2BqxKaQuE6uW vooyg4ymiEGWVUet1G8SD+rqvyNH4QrvnEIaFHxOhESip7vMz39ScLpNLbL1QpOlPW/tFIzNHS3q d2XRNYG5Sv9RcGE+T4qbLtsjjJbi6sL7Ls/f/X9ftTyhxvxWkf8KW37iKrueKsxw2HqolH7GM6FX 5UfNAwAu4ZifkpmZzU1slBhyWwaQPEPPZRsWoTb7q8hmgv6Nv3Hg9rmA1/VPBIOQ6SKRkHXG0Hhm q1dOFoAFI411+a/9nWm5rcVjGcIWZ2v/43Yksq60jExipA4l5uv9/+Hm33mbgmCszdj/Dthf13tg Av2O83hLJ0exTqfrlwIDAQABo4IBrTCCAakwDwYDVR0TAQH/BAUwAwEB/zAOBgNVHQ8BAf8EBAMC AQYwHQYDVR0OBBYEFFNy7ZKc4NrLAVx8fpY1TvLUuFGCMB8GA1UdIwQYMBaAFE4L7xqkQFulF2mH MMo0aEPQQa7yMGYGCCsGAQUFBwEBBFowWDAnBggrBgEFBQcwAYYbaHR0cDovL29jc3Auc3RhcnRz c2wuY29tL2NhMC0GCCsGAQUFBzAChiFodHRwOi8vd3d3LnN0YXJ0c3NsLmNvbS9zZnNjYS5jcnQw WwYDVR0fBFQwUjAnoCWgI4YhaHR0cDovL3d3dy5zdGFydHNzbC5jb20vc2ZzY2EuY3JsMCegJaAj hiFodHRwOi8vY3JsLnN0YXJ0c3NsLmNvbS9zZnNjYS5jcmwwgYAGA1UdIAR5MHcwdQYLKwYBBAGB tTcBAgEwZjAuBggrBgEFBQcCARYiaHR0cDovL3d3dy5zdGFydHNzbC5jb20vcG9saWN5LnBkZjA0 BggrBgEFBQcCARYoaHR0cDovL3d3dy5zdGFydHNzbC5jb20vaW50ZXJtZWRpYXRlLnBkZjANBgkq hkiG9w0BAQUFAAOCAgEACoMIfXirLAZcuGOMXq4cuSN3TaFx2H2GvD5VSy/6rV55BYHbWNaPeQn3 oBSU8KgQZn/Kck1JxbLpAxVCNtsxeW1R87ifhsYZ0qjdrA9anrW2MAWCtosmAOT4OxK9QPoSjCMx M3HbkZCDJgnlE8jMopH21BbyAYr7b5EfGRQJNtgWcvqSXwKHnTutR08+Kkn0KAkXCzeQNLeA5LlY UzFyM7kPAp8pIRMQ+seHunmyG642S2+y/qHEdMuGIwpfz3eDF1PdctL04qYK/zu+Qg1Bw0RwgigV Zs/0c5HP2/e9DBHh7eSwtzYlk4AUr6yxLlcwSjOfOmKEQ/Q8tzh0IFiNu9IPuTGAPBn4CPxD0+Ru 8T2wg8/s43R/PT3kd1OEqOJUl7q+h+r6fpvU0Fzxd2tC8Ga6fDEPme+1Nbi+03pVjuZQKbGwKJ66 gEn06WqaxVZC+J8hh/jR0k9mST1iAZPNYulcNJ8tKmVtjYsv0L1TSm2+NwON58tO+pIVzu3DWwSE XSf+qkDavQam+QtEOZxLBXI++aMUEapSn+k3Lxm48ZCYfAWLb/Xj7F5JQMbZvCexglAbYR0kIHqW 5DnsYSdMD/IplJMojx0NBrxJ3fN9dvX2Y6BIXRsF1du4qESm4/3CKuyUV7p9DW3mPlHTGLvYxnyK Qy7VFBkoLINszBrOUeIxggNvMIIDawIBATCBlDCBjDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0 YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcx ODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENB AgMN7zcwCQYFKw4DAhoFAKCCAa8wGAYJKoZIhvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0B CQUxDxcNMTUxMTA4MTIwMDMzWjAjBgkqhkiG9w0BCQQxFgQUYfSnKpg1S6ed/2i72x2Un2/4hCAw gaUGCSsGAQQBgjcQBDGBlzCBlDCBjDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0YXJ0Q29tIEx0 ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcxODA2BgNVBAMT L1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENBAgMN7zcwgacG CyqGSIb3DQEJEAILMYGXoIGUMIGMMQswCQYDVQQGEwJJTDEWMBQGA1UEChMNU3RhcnRDb20gTHRk LjErMCkGA1UECxMiU2VjdXJlIERpZ2l0YWwgQ2VydGlmaWNhdGUgU2lnbmluZzE4MDYGA1UEAxMv U3RhcnRDb20gQ2xhc3MgMSBQcmltYXJ5IEludGVybWVkaWF0ZSBDbGllbnQgQ0ECAw3vNzANBgkq hkiG9w0BAQEFAASCAQBaXi/qUcthP+JM9CYMWXtmHEmPwZjRVImIJmP1kEGW6bfc4cjHCnEL/GiA 8MkZuiBHjPCiO97mIl+goQWUxAUgfAANMispnWltDBeR/Yv4LifQ5hxtXYdKCGI+npGkN3csCNBL Ba9jSy0p09fSMsYLESWT2jFbuvzIQriHfpx1fx8YozLt/Xxw1hFDD66T5fYweq+TvcD2KqqHEnQc LtRoeHcuT9CDebutXz0in7GRZi0ce0fc36S+gVcfnubY5t3ajIhMkuechiXC8n4SxIgRFqVVh6Ul Nrbu/75pGMh0ZSUoDFIS7X87zIZaEQk3AYevxuje+bRCMWfubMEgJjuAAAAAAAAA --=-sfIFhvCLM1NIM5uxtI47-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/