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Thu, 10 Sep 2020 08:55:08 +0000 (UTC) Subject: Re: VHOST_USER_PROTOCOL_F_VDPA To: Stefan Hajnoczi References: <20200821110822.GA205318@stefanha-x1.localdomain> From: Maxime Coquelin Autocrypt: addr=maxime.coquelin@redhat.com; keydata= mQINBFOEQQIBEADjNLYZZqghYuWv1nlLisptPJp+TSxE/KuP7x47e1Gr5/oMDJ1OKNG8rlNg kLgBQUki3voWhUbMb69ybqdMUHOl21DGCj0BTU3lXwapYXOAnsh8q6RRM+deUpasyT+Jvf3a gU35dgZcomRh5HPmKMU4KfeA38cVUebsFec1HuJAWzOb/UdtQkYyZR4rbzw8SbsOemtMtwOx YdXodneQD7KuRU9IhJKiEfipwqk2pufm2VSGl570l5ANyWMA/XADNhcEXhpkZ1Iwj3TWO7XR uH4xfvPl8nBsLo/EbEI7fbuUULcAnHfowQslPUm6/yaGv6cT5160SPXT1t8U9QDO6aTSo59N jH519JS8oeKZB1n1eLDslCfBpIpWkW8ZElGkOGWAN0vmpLfdyiqBNNyS3eGAfMkJ6b1A24un /TKc6j2QxM0QK4yZGfAxDxtvDv9LFXec8ENJYsbiR6WHRHq7wXl/n8guyh5AuBNQ3LIK44x0 KjGXP1FJkUhUuruGyZsMrDLBRHYi+hhDAgRjqHgoXi5XGETA1PAiNBNnQwMf5aubt+mE2Q5r qLNTgwSo2dpTU3+mJ3y3KlsIfoaxYI7XNsPRXGnZi4hbxmeb2NSXgdCXhX3nELUNYm4ArKBP LugOIT/zRwk0H0+RVwL2zHdMO1Tht1UOFGfOZpvuBF60jhMzbQARAQABtCxNYXhpbWUgQ29x dWVsaW4gPG1heGltZS5jb3F1ZWxpbkByZWRoYXQuY29tPokCOAQTAQIAIgUCV3u/5QIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQyjiNKEaHD4ma2g/+P+Hg9WkONPaY1J4AR7Uf kBneosS4NO3CRy0x4WYmUSLYMLx1I3VH6SVjqZ6uBoYy6Fs6TbF6SHNc7QbB6Qjo3neqnQR1 71Ua1MFvIob8vUEl3jAR/+oaE1UJKrxjWztpppQTukIk4oJOmXbL0nj3d8dA2QgHdTyttZ1H xzZJWWz6vqxCrUqHU7RSH9iWg9R2iuTzii4/vk1oi4Qz7y/q8ONOq6ffOy/t5xSZOMtZCspu Mll2Szzpc/trFO0pLH4LZZfz/nXh2uuUbk8qRIJBIjZH3ZQfACffgfNefLe2PxMqJZ8mFJXc RQO0ONZvwoOoHL6CcnFZp2i0P5ddduzwPdGsPq1bnIXnZqJSl3dUfh3xG5ArkliZ/++zGF1O wvpGvpIuOgLqjyCNNRoR7cP7y8F24gWE/HqJBXs1qzdj/5Hr68NVPV1Tu/l2D1KMOcL5sOrz 2jLXauqDWn1Okk9hkXAP7+0Cmi6QwAPuBT3i6t2e8UdtMtCE4sLesWS/XohnSFFscZR6Vaf3 gKdWiJ/fW64L6b9gjkWtHd4jAJBAIAx1JM6xcA1xMbAFsD8gA2oDBWogHGYcScY/4riDNKXi lw92d6IEHnSf6y7KJCKq8F+Jrj2BwRJiFKTJ6ChbOpyyR6nGTckzsLgday2KxBIyuh4w+hMq TGDSp2rmWGJjASq5Ag0EVPSbkwEQAMkaNc084Qvql+XW+wcUIY+Dn9A2D1gMr2BVwdSfVDN7 0ZYxo9PvSkzh6eQmnZNQtl8WSHl3VG3IEDQzsMQ2ftZn2sxjcCadexrQQv3Lu60Tgj7YVYRM H+fLYt9W5YuWduJ+FPLbjIKynBf6JCRMWr75QAOhhhaI0tsie3eDsKQBA0w7WCuPiZiheJaL 4MDe9hcH4rM3ybnRW7K2dLszWNhHVoYSFlZGYh+MGpuODeQKDS035+4H2rEWgg+iaOwqD7bg CQXwTZ1kSrm8NxIRVD3MBtzp9SZdUHLfmBl/tLVwDSZvHZhhvJHC6Lj6VL4jPXF5K2+Nn/Su CQmEBisOmwnXZhhu8ulAZ7S2tcl94DCo60ReheDoPBU8PR2TLg8rS5f9w6mLYarvQWL7cDtT d2eX3Z6TggfNINr/RTFrrAd7NHl5h3OnlXj7PQ1f0kfufduOeCQddJN4gsQfxo/qvWVB7PaE 1WTIggPmWS+Xxijk7xG6x9McTdmGhYaPZBpAxewK8ypl5+yubVsE9yOOhKMVo9DoVCjh5To5 aph7CQWfQsV7cd9PfSJjI2lXI0dhEXhQ7lRCFpf3V3mD6CyrhpcJpV6XVGjxJvGUale7+IOp sQIbPKUHpB2F+ZUPWds9yyVxGwDxD8WLqKKy0WLIjkkSsOb9UBNzgRyzrEC9lgQ/ABEBAAGJ Ah8EGAECAAkFAlT0m5MCGwwACgkQyjiNKEaHD4nU8hAAtt0xFJAy0sOWqSmyxTc7FUcX+pbD KVyPlpl6urKKMk1XtVMUPuae/+UwvIt0urk1mXi6DnrAN50TmQqvdjcPTQ6uoZ8zjgGeASZg jj0/bJGhgUr9U7oG7Hh2F8vzpOqZrdd65MRkxmc7bWj1k81tOU2woR/Gy8xLzi0k0KUa8ueB iYOcZcIGTcs9CssVwQjYaXRoeT65LJnTxYZif2pfNxfINFzCGw42s3EtZFteczClKcVSJ1+L +QUY/J24x0/ocQX/M1PwtZbB4c/2Pg/t5FS+s6UB1Ce08xsJDcwyOPIH6O3tccZuriHgvqKP yKz/Ble76+NFlTK1mpUlfM7PVhD5XzrDUEHWRTeTJSvJ8TIPL4uyfzhjHhlkCU0mw7Pscyxn DE8G0UYMEaNgaZap8dcGMYH/96EfE5s/nTX0M6MXV0yots7U2BDb4soLCxLOJz4tAFDtNFtA wLBhXRSvWhdBJZiig/9CG3dXmKfi2H+wdUCSvEFHRpgo7GK8/Kh3vGhgKmnnxhl8ACBaGy9n fxjSxjSO6rj4/MeenmlJw1yebzkX8ZmaSi8BHe+n6jTGEFNrbiOdWpJgc5yHIZZnwXaW54QT UhhSjDL1rV2B4F28w30jYmlRmm2RdN7iCZfbyP3dvFQTzQ4ySquuPkIGcOOHrvZzxbRjzMx1 Mwqu3GQ= Message-ID: Date: Thu, 10 Sep 2020 10:55:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200821110822.GA205318@stefanha-x1.localdomain> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=maxime.coquelin@redhat.com X-Mimecast-Spam-Score: 0.326 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="9HUv2wN3GCvIAPg2lMY8RjaJtAVT7IFbV" Received-SPF: pass client-ip=205.139.110.120; envelope-from=maxime.coquelin@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/10 01:23:25 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -56 X-Spam_score: -5.7 X-Spam_bar: ----- X-Spam_report: (-5.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-3.576, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Chenbo Xia , Cindy Lu , "Michael S. Tsirkin" , jasowang@redhat.com, qemu-devel@nongnu.org, Raphael Norwitz , kraxel@redhat.com, =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Changpeng Liu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --9HUv2wN3GCvIAPg2lMY8RjaJtAVT7IFbV Content-Type: multipart/mixed; boundary="bpL1qVBHI2ZbOkeBHl3G9X6Bq8VUyLK6j"; protected-headers="v1" From: Maxime Coquelin To: Stefan Hajnoczi Cc: Chenbo Xia , Cindy Lu , "Michael S. Tsirkin" , jasowang@redhat.com, qemu-devel@nongnu.org, Raphael Norwitz , kraxel@redhat.com, =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Changpeng Liu Message-ID: Subject: Re: VHOST_USER_PROTOCOL_F_VDPA References: <20200821110822.GA205318@stefanha-x1.localdomain> In-Reply-To: <20200821110822.GA205318@stefanha-x1.localdomain> --bpL1qVBHI2ZbOkeBHl3G9X6Bq8VUyLK6j Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable Hi Stefan, On 8/21/20 1:08 PM, Stefan Hajnoczi wrote: > The first vDPA ioctls have been added to the vhost-user protocol and I > wonder if it's time to fully change the vhost-user protocol's focus to > providing a full VIRTIO device model like vDPA does. >=20 > Initially vhost-user was just used for vhost-net. As a result it didn't > need the full VIRTIO device model including the configuration space and > device status register. >=20 > Over the years device-specific messages were added to extend vhost-user > to cover more of the VIRTIO device model. vhost-user-blk needed > configuration space support, for example. >=20 > The problem for VMMs and device backend implementors is that the > protocol is currently positioned halfway between the original vhost-net > approach and the full VIRTIO device model. Even if a VMM implements > VHOST_USER_GET_CONFIG, it can only expect it to work with > vhost-user-blk, not vhost-user-net. Similarly, a vhost-user-net device > backend cannot implement VHOST_USER_GET_CONFIG and expect all VMMs to > allow it to participate in configuration space emulation because > existing VMMs won't send that message. >=20 > The current approach where each device type uses a undocumented subset > of vhost-user messages is really messy. VMM and device backend > implementors have to look at existing implementations to know what is > expected for a given device type. It would be nice to switch to the > VIRTIO device model so that the VIRTIO specification can be used as the > reference for how device types work. >=20 > Now that vDPA is here and extends the kernel vhost ioctls with a full > VIRTIO device model, it might be a good time to revise the vhost-user > protocol. >=20 > A vdpa-user protocol (or vhost-user 2.0) would replace the current mess > with a full VIRTIO device model. Both VMMs and device backends would > require changes to support this, but it would be a cleaner path forward > for the vhost-user protocol. >=20 > One way of doing this would be a new VHOST_USER_PROTOCOL_F_VDPA feature > bit that indicates all the currently existing Linux vDPA ioctl messages > are available. Legacy vhost-user messages with overlapping functionality > must not be used when this bit is set. Most importantly, device backends > need to implement the full VIRTIO device model, regardless of device > type (net, blk, scsi, etc). >=20 > The device type most affected by this change would be virtio-net. The > other device types are already closer to the full VIRTIO device model. >=20 > I wanted to share this idea in case someone is currently trying to > figure out how to add more VIRTIO device model functionality to > vhost-user. >=20 > Stefan >=20 I understand the need and like the idea. Maxime --bpL1qVBHI2ZbOkeBHl3G9X6Bq8VUyLK6j-- --9HUv2wN3GCvIAPg2lMY8RjaJtAVT7IFbV Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEE3P4B0hLzOlwaL+KyjiNKEaHD4kFAl9Z6eoACgkQyjiNKEaH D4lPwRAAkqeHcgVoj9qZ34KWw8UhRoOfkPhNO9B5cqFI0J2lqeKzgnOvkm5aTa8C luQg+tag3Sz9IMEGTtONOoGhu5B+2uuEyS22ibYjmWZK386rzBkRk31r192BbSHe bXlAXiRGcfZC0sNTtWfn18pAL+wdDYRllLbNEztPJA+fkHlo3Dl8sv0Jc6HwJXUh dtsJ1JB1kz6cUdzNziHk9pu3d9Ul8BvTPfvgL2WiDPEhGwga6vsHmWF7ZKQ++pRn VA9NY8tcmIbfWR6uxQWQiEMoRsW4yTYWrAlOmz+8lVQj5ia6QwQhfnt25jYs+Atp FibHjWeAAxj/4akoRGagkqSEjwA143jOoSkOjJqWL8VIJUTxphS+HCHkgB+As6/q vYFd3qtuzAIGmHUWiPWXeuoV9QEE0KAokwyBU3uLl28xoBhfoaQI404GYHuS8uGx rfpXQWK5VO7muHGbgkCxxnk/mRj7XsP5IUP2SVB5VLuCtzD9UaEEKMhPjDBgTIbR 8jKEmkKRqhb6XIiQPGFMvVwb+6VUchfqJB4Fezks83/Oic0I2FFNa8txMCqnC7Zz lL1lS7TTvR6pguu+3D/oliYMl8dDF3SJ+/NqWo+StiYvWwBbsT+Utf2373nl86uX VRmPSRc3dmIzxgqN3YAAklSq2/z89KPzU5W2bXMfkrq/dgJ+APw= =srOi -----END PGP SIGNATURE----- --9HUv2wN3GCvIAPg2lMY8RjaJtAVT7IFbV--