From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 8D6C96B0272 for ; Fri, 6 Oct 2017 19:10:52 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id u78so17299285wmd.4 for ; Fri, 06 Oct 2017 16:10:52 -0700 (PDT) Received: from twosheds.infradead.org (twosheds.infradead.org. [2001:8b0:10b:1:21d:7dff:fe04:dbe2]) by mx.google.com with ESMTPS id p77si2213257wma.88.2017.10.06.16.10.51 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 06 Oct 2017 16:10:51 -0700 (PDT) Message-ID: <1507331434.29211.439.camel@infradead.org> Subject: Re: [PATCH v7 07/12] dma-mapping: introduce dma_has_iommu() From: David Woodhouse In-Reply-To: References: <150732931273.22363.8436792888326501071.stgit@dwillia2-desk3.amr.corp.intel.com> <150732935473.22363.1853399637339625023.stgit@dwillia2-desk3.amr.corp.intel.com> <1507329939.29211.434.camel@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-309WFqKqv3GM7Se1C2w/" Date: Sat, 07 Oct 2017 00:10:34 +0100 Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: "linux-nvdimm@lists.01.org" , Jan Kara , Ashok Raj , "Darrick J. Wong" , linux-rdma@vger.kernel.org, Greg Kroah-Hartman , Joerg Roedel , Dave Chinner , linux-xfs@vger.kernel.org, Linux MM , Jeff Moyer , Linux API , linux-fsdevel , Ross Zwisler , Robin Murphy , Christoph Hellwig , Marek Szyprowski --=-309WFqKqv3GM7Se1C2w/ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2017-10-06 at 15:52 -0700, Dan Williams wrote: > On Fri, Oct 6, 2017 at 3:45 PM, David Woodhouse wro= te: > >=20 > > On Fri, 2017-10-06 at 15:35 -0700, Dan Williams wrote: > > >=20 > > > Add a helper to determine if the dma mappings set up for a given devi= ce > > > are backed by an iommu. In particular, this lets code paths know that= a > > > dma_unmap operation will revoke access to memory if the device can no= t > > > otherwise be quiesced. The need for this knowledge is driven by a nee= d > > > to make RDMA transfers to DAX mappings safe. If the DAX file's block = map > > > changes we need to be to reliably stop accesses to blocks that have b= een > > > freed or re-assigned to a new file. > > "a dma_unmap operation revoke access to memory"... but it's OK that the > > next *map* will give the same DMA address to someone else, right? > > I'm assuming the next map will be to other physical addresses and a > different requester device since the memory is still registered > exclusively. I meant the next map for this device/group. It may well use the same virtual DMA address as the one you just unmapped, yet actually map to a different physical address. So if the DMA still occurs to the "old" address, that isn't revoked at all =E2=80=94 = it's just going to the wrong physical location. And if you are sure that the DMA will never happen, why do you need to revoke the mapping in the first place? --=-309WFqKqv3GM7Se1C2w/ Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDzUw ggSvMIIDl6ADAgECAhEA4CPLFRKDU4mtYW56VGdrITANBgkqhkiG9w0BAQsFADBvMQswCQYDVQQG EwJTRTEUMBIGA1UEChMLQWRkVHJ1c3QgQUIxJjAkBgNVBAsTHUFkZFRydXN0IEV4dGVybmFsIFRU UCBOZXR3b3JrMSIwIAYDVQQDExlBZGRUcnVzdCBFeHRlcm5hbCBDQSBSb290MB4XDTE0MTIyMjAw MDAwMFoXDTIwMDUzMDEwNDgzOFowgZsxCzAJBgNVBAYTAkdCMRswGQYDVQQIExJHcmVhdGVyIE1h bmNoZXN0ZXIxEDAOBgNVBAcTB1NhbGZvcmQxGjAYBgNVBAoTEUNPTU9ETyBDQSBMaW1pdGVkMUEw PwYDVQQDEzhDT01PRE8gU0hBLTI1NiBDbGllbnQgQXV0aGVudGljYXRpb24gYW5kIFNlY3VyZSBF bWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAImxDdp6UxlOcFIdvFamBia3 uEngludRq/HwWhNJFaO0jBtgvHpRQqd5jKQi3xdhTpHVdiMKFNNKAn+2HQmAbqUEPdm6uxb+oYep 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