From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9B6A31F03FF; Thu, 3 Apr 2025 07:37:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743665845; cv=none; b=uX4iQzMxNfLL/dpgFXIRdWr6vtdNdySnBxlWboB0j3CTaI9iazn/kcGbNTXC519+HwVIqe+mzkEzi72/dfxYAKupnrRTl3pahSwWhh1mnrSn/2sh1hIGR3T9uYaWAJqbIZz6RzG37KZIR+hatZAYT99TV3WtRy6byhu87t4F+T8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743665845; c=relaxed/simple; bh=daFrifOQnUKqeZLt8gCXV2HXtiu3gXL2lFRtxnrujnY=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Hj+XbRfEcb3OqfTbjXx2VyzptRL2VA1o3dBX2hJ0ahZSrNaMCNbnocRdI2jjIqHLINmeyI3wIVSipIjoBcoj5vXSc/zOXrxer7R0xQ+Kn2MHneS4ENZ0czw9GcL9sFTe3aJQ9Xt5oIBaauKbWa8eZVkyL3WFi82s/wPhjQQeats= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=k4B7cm1n; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="k4B7cm1n" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=daFrifOQnUKqeZLt8gCXV2HXtiu3gXL2lFRtxnrujnY=; b=k4B7cm1nXXePYINmwme71EL0ek pb/7Nr8ovYbyU8QvSO4Olza34/mRdxUHBzUrtUsXz93EHGGX+odG4WIWcpPTyHfyrqW3Y70OYaWmH XLI11YQypK5gk3+99lqKGDrzj38JVCwnYvWoSA7LV59Ptdm0m3uuq6II6bL3FOJdglreV/KjjcmfK J/g8lvI4k+WkVdYUt/Qw4TB9cP5RTMoJk0jsHBUi1y330otVp8B8pzWNj70fJINmb94CfXkVO8mDq rYvurHu37lyA2HksLHwb4hhZTHGkKh7Jl7l9P1ft+EZXLFEJqQd2UTRu6Riay/DcYD3Akyt8MC5wq lMzFnPvg==; Received: from [172.31.31.145] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.1 #2 (Red Hat Linux)) id 1u0F8a-000000079Kd-0t3e; Thu, 03 Apr 2025 07:37:20 +0000 Message-ID: <06465bcf4422d088df2a0ce9cdb09767dac83118.camel@infradead.org> Subject: Re: [RFC PATCH 1/3] content: Add VIRTIO_F_SWIOTLB to negotiate use of SWIOTLB bounce buffers From: David Woodhouse To: Christoph Hellwig Cc: "Michael S. Tsirkin" , virtio-comment@lists.linux.dev, Claire Chang , linux-devicetree , Rob Herring , =?ISO-8859-1?Q?J=F6rg?= Roedel , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, graf@amazon.de Date: Thu, 03 Apr 2025 08:37:20 +0100 In-Reply-To: References: <20250402112410.2086892-1-dwmw2@infradead.org> <20250402112410.2086892-2-dwmw2@infradead.org> <20250402105137-mutt-send-email-mst@kernel.org> <19ba662feeb93157bc8a03fb0b11cb5f2eca5e40.camel@infradead.org> <20250402111901-mutt-send-email-mst@kernel.org> <6b3b047f1650d91abe5e523dd7f862c6f7ee6611.camel@infradead.org> <20250402114757-mutt-send-email-mst@kernel.org> <965ccf2f972c5d5f1f4edacb227f03171f20e887.camel@infradead.org> <20250402124131-mutt-send-email-mst@kernel.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-Dm2IGgDpk0mwAvqmmjXg" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-Dm2IGgDpk0mwAvqmmjXg Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2025-04-03 at 00:29 -0700, Christoph Hellwig wrote: > On Wed, Apr 02, 2025 at 06:10:53PM +0100, David Woodhouse wrote: > > > I know a bit more about PCI, and for PCI I prefer just not saying > > > anything. The platform already defines whether it is behind an iommu > > > or not, and duplication is not good. > >=20 > > Not a hill for me to die on I suppose, but I would personally prefer to > > spell it out in words of one syllable or fewer, to make *sure* that > > device and driver authors get it right even though it's "obvious". > >=20 > > After all, if we could trust them to do their thinking, we would never > > have had the awful situation that led to VIRTIO_F_ACCESS_PLATFORM > > existing in the first place; the legacy behaviour we get when that bit > > *isn't* set would never have happened. >=20 > You'll need to define the semanics for VIRTIO_F_ACCESS_PLATFORM only > then.=C2=A0=C2=A0 >=20 You mean the semantics for VIRTIO_F_ACCESS_PLATFORM only, without VIRTIO_F_SWIOTLB? Are those not defined already? > An the only sane answer there is: don't allow non-translated > regions at all an in a broader sense stop people to use > VIRTIO_F_ACCESS_PLATFORM at all or at least for anything that requires > a new feature bit. >=20 > > > For mmio it is my understanding that the "restricted" does the same > > > already? or is it required in the spec for some reason? > >=20 > > No, it's exactly the same. But I still don't trust driver authors to > > realise the obvious, or VMM implementations either for that matter. > >=20 > > I'm not sure I see the *harm* in spelling out explicitly for the hard- > > of-thinking. >=20 > Write a whitepaper than and explain how it maps to the existing perfectly > working features.=C2=A0 Note that VIRTIO_F_ACCESS_PLATFORM just like > everything in virtio would actually benefit from being turned into > proper spec language, but anecdotes about random use cases are not > helpful. Hm. I was just trying to point out what seemed obvious, that when a PCI device does 'DMA' to an address region which is actually within one of its *own* BARs, it isn't going to reach the PCI bus and get translated by an IOMMU. If it's causing this much contention, I'll just drop it. It didn't *change* anything anyway, except hopefully avoiding bugs in implementations. --=-Dm2IGgDpk0mwAvqmmjXg Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 aDJAwtycb8yXtILj+TvfhLFhafxroXrflspavejQkEiHjNjtHnwbZ+o43g0/yxjwnarGI3kgcak7 nnI9/8Lqpq79tLHYwLajotwLiGTB71AGN5xK+tzB+D4eN9lXayrjcszgbOv2ZCgzExQUAIt98mre 8EggKs9mwtEuKAhYBIP/0K6WsoMnQCcCAwEAAaOCAVwwggFYMBIGA1UdEwEB/wQIMAYBAf8CAQAw HQYDVR0OBBYEFIlICOogTndrhuWByNfhjWSEf/xwMB8GA1UdIwQYMBaAFEXroq/0ksuCMS1Ri6en IZ3zbcgPMA4GA1UdDwEB/wQEAwIBhjAdBgNVHSUEFjAUBggrBgEFBQcDBAYIKwYBBQUHAwIweQYI KwYBBQUHAQEEbTBrMCQGCCsGAQUFBzABhhhodHRwOi8vb2NzcC5kaWdpY2VydC5jb20wQwYIKwYB BQUHMAKGN2h0dHA6Ly9jYWNlcnRzLmRpZ2ljZXJ0LmNvbS9EaWdpQ2VydEFzc3VyZWRJRFJvb3RD QS5jcnQwRQYDVR0fBD4wPDA6oDigNoY0aHR0cDovL2NybDMuZGlnaWNlcnQuY29tL0RpZ2lDZXJ0 QXNzdXJlZElEUm9vdENBLmNybDARBgNVHSAECjAIMAYGBFUdIAAwDQYJKoZIhvcNAQELBQADggEB ACiagCqvNVxOfSd0uYfJMiZsOEBXAKIR/kpqRp2YCfrP4Tz7fJogYN4fxNAw7iy/bPZcvpVCfe/H /CCcp3alXL0I8M/rnEnRlv8ItY4MEF+2T/MkdXI3u1vHy3ua8SxBM8eT9LBQokHZxGUX51cE0kwa uEOZ+PonVIOnMjuLp29kcNOVnzf8DGKiek+cT51FvGRjV6LbaxXOm2P47/aiaXrDD5O0RF5SiPo6 xD1/ClkCETyyEAE5LRJlXtx288R598koyFcwCSXijeVcRvBB1cNOLEbg7RMSw1AGq14fNe2cH1HG W7xyduY/ydQt6gv5r21mDOQ5SaZSWC/ZRfLDuEYwggWbMIIEg6ADAgECAhAH5JEPagNRXYDiRPdl c1vgMA0GCSqGSIb3DQEBCwUAMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYD VQQDExdWZXJva2V5IFNlY3VyZSBFbWFpbCBHMjAeFw0yNDEyMzAwMDAwMDBaFw0yODAxMDQyMzU5 NTlaMB4xHDAaBgNVBAMME2R3bXcyQGluZnJhZGVhZC5vcmcwggIiMA0GCSqGSIb3DQEBAQUAA4IC DwAwggIKAoICAQDali7HveR1thexYXx/W7oMk/3Wpyppl62zJ8+RmTQH4yZeYAS/SRV6zmfXlXaZ sNOE6emg8WXLRS6BA70liot+u0O0oPnIvnx+CsMH0PD4tCKSCsdp+XphIJ2zkC9S7/yHDYnqegqt w4smkqUqf0WX/ggH1Dckh0vHlpoS1OoxqUg+ocU6WCsnuz5q5rzFsHxhD1qGpgFdZEk2/c//ZvUN i12vPWipk8TcJwHw9zoZ/ZrVNybpMCC0THsJ/UEVyuyszPtNYeYZAhOJ41vav1RhZJzYan4a1gU0 kKBPQklcpQEhq48woEu15isvwWh9/+5jjh0L+YNaN0I//nHSp6U9COUG9Z0cvnO8FM6PTqsnSbcc 0j+GchwOHRC7aP2t5v2stVx3KbptaYEzi4MQHxm/0+HQpMEVLLUiizJqS4PWPU6zfQTOMZ9uLQRR ci+c5xhtMEBszlQDOvEQcyEG+hc++fH47K+MmZz21bFNfoBxLP6bjR6xtPXtREF5lLXxp+CJ6KKS blPKeVRg/UtyJHeFKAZXO8Zeco7TZUMVHmK0ZZ1EpnZbnAhKE19Z+FJrQPQrlR0gO3lBzuyPPArV hvWxjlO7S4DmaEhLzarWi/ze7EGwWSuI2eEa/8zU0INUsGI4ywe7vepQz7IqaAovAX0d+f1YjbmC VsAwjhLmveFjNwIDAQABo4IBsDCCAawwHwYDVR0jBBgwFoAUiUgI6iBOd2uG5YHI1+GNZIR//HAw HQYDVR0OBBYEFFxiGptwbOfWOtMk5loHw7uqWUOnMDAGA1UdEQQpMCeBE2R3bXcyQGluZnJhZGVh ZC5vcmeBEGRhdmlkQHdvb2Rob3Uuc2UwFAYDVR0gBA0wCzAJBgdngQwBBQEBMA4GA1UdDwEB/wQE AwIF4DAdBgNVHSUEFjAUBggrBgEFBQcDAgYIKwYBBQUHAwQwewYDVR0fBHQwcjA3oDWgM4YxaHR0 cDovL2NybDMuZGlnaWNlcnQuY29tL1Zlcm9rZXlTZWN1cmVFbWFpbEcyLmNybDA3oDWgM4YxaHR0 cDovL2NybDQuZGlnaWNlcnQuY29tL1Zlcm9rZXlTZWN1cmVFbWFpbEcyLmNybDB2BggrBgEFBQcB AQRqMGgwJAYIKwYBBQUHMAGGGGh0dHA6Ly9vY3NwLmRpZ2ljZXJ0LmNvbTBABggrBgEFBQcwAoY0 aHR0cDovL2NhY2VydHMuZGlnaWNlcnQuY29tL1Zlcm9rZXlTZWN1cmVFbWFpbEcyLmNydDANBgkq hkiG9w0BAQsFAAOCAQEAQXc4FPiPLRnTDvmOABEzkIumojfZAe5SlnuQoeFUfi+LsWCKiB8Uextv iBAvboKhLuN6eG/NC6WOzOCppn4mkQxRkOdLNThwMHW0d19jrZFEKtEG/epZ/hw/DdScTuZ2m7im 8ppItAT6GXD3aPhXkXnJpC/zTs85uNSQR64cEcBFjjoQDuSsTeJ5DAWf8EMyhMuD8pcbqx5kRvyt JPsWBQzv1Dsdv2LDPLNd/JUKhHSgr7nbUr4+aAP2PHTXGcEBh8lTeYea9p4d5k969pe0OHYMV5aL xERqTagmSetuIwolkAuBCzA9vulg8Y49Nz2zrpUGfKGOD0FMqenYxdJHgDCCBZswggSDoAMCAQIC EAfkkQ9qA1FdgOJE92VzW+AwDQYJKoZIhvcNAQELBQAwQTELMAkGA1UEBhMCQVUxEDAOBgNVBAoT B1Zlcm9rZXkxIDAeBgNVBAMTF1Zlcm9rZXkgU2VjdXJlIEVtYWlsIEcyMB4XDTI0MTIzMDAwMDAw MFoXDTI4MDEwNDIzNTk1OVowHjEcMBoGA1UEAwwTZHdtdzJAaW5mcmFkZWFkLm9yZzCCAiIwDQYJ KoZIhvcNAQEBBQADggIPADCCAgoCggIBANqWLse95HW2F7FhfH9bugyT/danKmmXrbMnz5GZNAfj Jl5gBL9JFXrOZ9eVdpmw04Tp6aDxZctFLoEDvSWKi367Q7Sg+ci+fH4KwwfQ8Pi0IpIKx2n5emEg nbOQL1Lv/IcNiep6Cq3DiyaSpSp/RZf+CAfUNySHS8eWmhLU6jGpSD6hxTpYKye7PmrmvMWwfGEP WoamAV1kSTb9z/9m9Q2LXa89aKmTxNwnAfD3Ohn9mtU3JukwILRMewn9QRXK7KzM+01h5hkCE4nj W9q/VGFknNhqfhrWBTSQoE9CSVylASGrjzCgS7XmKy/BaH3/7mOOHQv5g1o3Qj/+cdKnpT0I5Qb1 nRy+c7wUzo9OqydJtxzSP4ZyHA4dELto/a3m/ay1XHcpum1pgTOLgxAfGb/T4dCkwRUstSKLMmpL g9Y9TrN9BM4xn24tBFFyL5znGG0wQGzOVAM68RBzIQb6Fz758fjsr4yZnPbVsU1+gHEs/puNHrG0 9e1EQXmUtfGn4InoopJuU8p5VGD9S3Ikd4UoBlc7xl5yjtNlQxUeYrRlnUSmdlucCEoTX1n4UmtA 9CuVHSA7eUHO7I88CtWG9bGOU7tLgOZoSEvNqtaL/N7sQbBZK4jZ4Rr/zNTQg1SwYjjLB7u96lDP sipoCi8BfR35/ViNuYJWwDCOEua94WM3AgMBAAGjggGwMIIBrDAfBgNVHSMEGDAWgBSJSAjqIE53 a4blgcjX4Y1khH/8cDAdBgNVHQ4EFgQUXGIam3Bs59Y60yTmWgfDu6pZQ6cwMAYDVR0RBCkwJ4ET ZHdtdzJAaW5mcmFkZWFkLm9yZ4EQZGF2aWRAd29vZGhvdS5zZTAUBgNVHSAEDTALMAkGB2eBDAEF AQEwDgYDVR0PAQH/BAQDAgXgMB0GA1UdJQQWMBQGCCsGAQUFBwMCBggrBgEFBQcDBDB7BgNVHR8E dDByMDegNaAzhjFodHRwOi8vY3JsMy5kaWdpY2VydC5jb20vVmVyb2tleVNlY3VyZUVtYWlsRzIu Y3JsMDegNaAzhjFodHRwOi8vY3JsNC5kaWdpY2VydC5jb20vVmVyb2tleVNlY3VyZUVtYWlsRzIu Y3JsMHYGCCsGAQUFBwEBBGowaDAkBggrBgEFBQcwAYYYaHR0cDovL29jc3AuZGlnaWNlcnQuY29t MEAGCCsGAQUFBzAChjRodHRwOi8vY2FjZXJ0cy5kaWdpY2VydC5jb20vVmVyb2tleVNlY3VyZUVt YWlsRzIuY3J0MA0GCSqGSIb3DQEBCwUAA4IBAQBBdzgU+I8tGdMO+Y4AETOQi6aiN9kB7lKWe5Ch 4VR+L4uxYIqIHxR7G2+IEC9ugqEu43p4b80LpY7M4KmmfiaRDFGQ50s1OHAwdbR3X2OtkUQq0Qb9 6ln+HD8N1JxO5nabuKbymki0BPoZcPdo+FeRecmkL/NOzzm41JBHrhwRwEWOOhAO5KxN4nkMBZ/w QzKEy4PylxurHmRG/K0k+xYFDO/UOx2/YsM8s138lQqEdKCvudtSvj5oA/Y8dNcZwQGHyVN5h5r2 nh3mT3r2l7Q4dgxXlovERGpNqCZJ624jCiWQC4ELMD2+6WDxjj03PbOulQZ8oY4PQUyp6djF0keA MYIDuzCCA7cCAQEwVTBBMQswCQYDVQQGEwJBVTEQMA4GA1UEChMHVmVyb2tleTEgMB4GA1UEAxMX VmVyb2tleSBTZWN1cmUgRW1haWwgRzICEAfkkQ9qA1FdgOJE92VzW+AwDQYJYIZIAWUDBAIBBQCg ggE3MBgGCSqGSIb3DQEJAzELBgkqhkiG9w0BBwEwHAYJKoZIhvcNAQkFMQ8XDTI1MDQwMzA3Mzcy MFowLwYJKoZIhvcNAQkEMSIEIMtmfsqeCX9N3qgevLASUxzm1ZvQaBwhvaUDNH4OX9jdMGQGCSsG AQQBgjcQBDFXMFUwQTELMAkGA1UEBhMCQVUxEDAOBgNVBAoTB1Zlcm9rZXkxIDAeBgNVBAMTF1Zl cm9rZXkgU2VjdXJlIEVtYWlsIEcyAhAH5JEPagNRXYDiRPdlc1vgMGYGCyqGSIb3DQEJEAILMVeg VTBBMQswCQYDVQQGEwJBVTEQMA4GA1UEChMHVmVyb2tleTEgMB4GA1UEAxMXVmVyb2tleSBTZWN1 cmUgRW1haWwgRzICEAfkkQ9qA1FdgOJE92VzW+AwDQYJKoZIhvcNAQEBBQAEggIANRbeHrxM4Oiz V4pAnEXbF64INvM88AImr8IahqJywmQwCknr4QWHLWbWG95yoINWDu8OsI8zJqto2j00Z/L8Tsk2 Y89UBROmLC0Zz6vedrqtmxe/0otSWRi8UQckRsdGcegQn/AEJxAI6qQ5HzKJEozmKoXnpf4mSHjo 7vlKQ6GpX8zTwbkolZjX0M4gIJRzEuhRU9vqkJVP8GS0THTtKqFpHrENtXR0Gb7yqJwyTgHDpgk3 zkbiXBjG1NZku6jLmASycQVXrE8Z71tASqRiaFGUnl+pCrkf2JuMTzT4JmiMpmBLMEEnCzfvLlEK 2L0DbLOQuFlC1XVv6irUyRors1whBrqckM3WQCi7ruFV1/N68ic1ae33gGlKM0brXzZmStWruAQM tEZAfZAJor6XPv+Id/xeZH5ehH9Nl6KNG5OID8EJ/RXwUkfrCgADVc9bErrkp3qffvdLGpaJo1Cf 9mGc87rM5pO7u/CiKxq/aQOAsSaF61bhaCCbpTd7dvu6e2nros0sscbjhB1EnWX1dwkyQA7LF7WG CJ9CT2jrVLMmf5XYvB+t+7Btn+ZSRlmjoAeT5K+nj8UuI3/3JWpanxw7y63u8DabFyq2Hyann3Fo 7t0bT+MPcMV52KmcQJ9zedpIjSi9L/qdJ7EznXARgarUoTMXM8ENzXQ4fAwunXoAAAAAAAA= --=-Dm2IGgDpk0mwAvqmmjXg--