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auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="qj6oTXXpImQHk+rE" Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.199, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: virtio-fs@redhat.com, qemu-devel@nongnu.org, Vivek Goyal , groug@kaod.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --qj6oTXXpImQHk+rE Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jun 10, 2021 at 04:29:42PM +0100, Dr. David Alan Gilbert wrote: > * Dr. David Alan Gilbert (dgilbert@redhat.com) wrote: > > * Stefan Hajnoczi (stefanha@redhat.com) wrote: >=20 > >=20 > > > Instead I was thinking about VHOST_USER_DMA_READ/WRITE messages > > > containing the address (a device IOVA, it could just be a guest physi= cal > > > memory address in most cases) and the length. The WRITE message would > > > also contain the data that the vhost-user device wishes to write. The > > > READ message reply would contain the data that the device read from > > > QEMU. > > >=20 > > > QEMU would implement this using QEMU's address_space_read/write() API= s. > > >=20 > > > So basically just a new vhost-user protocol message to do a memcpy(), > > > but with guest addresses and vIOMMU support :). > >=20 > > This doesn't actually feel that hard - ignoring vIOMMU for a minute > > which I know very little about - I'd have to think where the data > > actually flows, probably the slave fd. > >=20 > > > The vhost-user device will need to do bounce buffering so using these > > > new messages is slower than zero-copy I/O to shared guest RAM. > >=20 > > I guess the theory is it's only in the weird corner cases anyway. The feature is also useful if DMA isolation is desirable (i.e. security/reliability are more important than performance). Once this new vhost-user protocol feature is available it will be possible to run vhost-user devices without shared memory or with limited shared memory (e.g. just the vring). > The direction I'm going is something like the following; > the idea is that the master will have to handle the requests on a > separate thread, to avoid any problems with side effects from the memory > accesses; the slave will then have to parkt he requests somewhere and > handle them later. >=20 >=20 > From 07aacff77c50c8a2b588b2513f2dfcfb8f5aa9df Mon Sep 17 00:00:00 2001 > From: "Dr. David Alan Gilbert" > Date: Thu, 10 Jun 2021 15:34:04 +0100 > Subject: [PATCH] WIP: vhost-user: DMA type interface >=20 > A DMA type interface where the slave can ask for a stream of bytes > to be read/written to the guests memory by the master. > The interface is asynchronous, since a request may have side effects > inside the guest. >=20 > Signed-off-by: Dr. David Alan Gilbert > --- > docs/interop/vhost-user.rst | 33 +++++++++++++++++++++++ > hw/virtio/vhost-user.c | 4 +++ > subprojects/libvhost-user/libvhost-user.h | 24 +++++++++++++++++ > 3 files changed, 61 insertions(+) Use of the word "RAM" in this patch is a little unclear since we need these new messages precisely when it's not ordinary guest RAM :-). Maybe referring to the address space is more general. > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst > index 9ebd05e2bf..b9b5322147 100644 > --- a/docs/interop/vhost-user.rst > +++ b/docs/interop/vhost-user.rst > @@ -1347,6 +1347,15 @@ Master message types > query the backend for its device status as defined in the Virtio > specification. > =20 > +``VHOST_USER_MEM_DATA`` > + :id: 41 > + :equivalent ioctl: N/A > + :slave payload: N/A > + :master payload: ``struct VhostUserMemReply`` > + > + This message is an asynchronous response to a ``VHOST_USER_SLAVE_MEM_A= CCESS`` > + message. Where the request was for the master to read data, this > + message will be followed by the data that was read. Please explain why this message is asynchronous. Implementors will need to understand the gotchas around deadlocks, etc. > =20 > Slave message types > ------------------- > @@ -1469,6 +1478,30 @@ Slave message types > The ``VHOST_USER_FS_FLAG_MAP_W`` flag must be set in the ``flags`` fie= ld to > write to the file from RAM. > =20 > +``VHOST_USER_SLAVE_MEM_ACCESS`` > + :id: 9 > + :equivalent ioctl: N/A > + :slave payload: ``struct VhostUserMemAccess`` > + :master payload: N/A > + > + Requests that the master perform a range of memory accesses on behalf > + of the slave that the slave can't perform itself. > + > + The ``VHOST_USER_MEM_FLAG_TO_MASTER`` flag must be set in the ``flags`= ` > + field for the slave to write data into the RAM of the master. In thi= s > + case the data to write follows the ``VhostUserMemAccess`` on the fd. > + The ``VHOST_USER_MEM_FLAG_FROM_MASTER`` flag must be set in the ``flag= s`` > + field for the slave to read data from the RAM of the master. > + > + When the master has completed the access it replies on the main fd wit= h > + a ``VHOST_USER_MEM_DATA`` message. > + > + The master is allowed to complete part of the request and reply statin= g > + the amount completed, leaving it to the slave to resend further compon= ents. > + This may happen to limit memory allocations in the master or to simpli= fy > + the implementation. > + > + > .. _reply_ack: > =20 > VHOST_USER_PROTOCOL_F_REPLY_ACK > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c > index 39a0e55cca..a3fefc4c1d 100644 > --- a/hw/virtio/vhost-user.c > +++ b/hw/virtio/vhost-user.c > @@ -126,6 +126,9 @@ typedef enum VhostUserRequest { > VHOST_USER_GET_MAX_MEM_SLOTS =3D 36, > VHOST_USER_ADD_MEM_REG =3D 37, > VHOST_USER_REM_MEM_REG =3D 38, > + VHOST_USER_SET_STATUS =3D 39, > + VHOST_USER_GET_STATUS =3D 40, > + VHOST_USER_MEM_DATA =3D 41, > VHOST_USER_MAX > } VhostUserRequest; > =20 > @@ -139,6 +142,7 @@ typedef enum VhostUserSlaveRequest { > VHOST_USER_SLAVE_FS_MAP =3D 6, > VHOST_USER_SLAVE_FS_UNMAP =3D 7, > VHOST_USER_SLAVE_FS_IO =3D 8, > + VHOST_USER_SLAVE_MEM_ACCESS =3D 9, > VHOST_USER_SLAVE_MAX > } VhostUserSlaveRequest; > =20 > diff --git a/subprojects/libvhost-user/libvhost-user.h b/subprojects/libv= host-user/libvhost-user.h > index eee611a2f6..b5444f4f6f 100644 > --- a/subprojects/libvhost-user/libvhost-user.h > +++ b/subprojects/libvhost-user/libvhost-user.h > @@ -109,6 +109,9 @@ typedef enum VhostUserRequest { > VHOST_USER_GET_MAX_MEM_SLOTS =3D 36, > VHOST_USER_ADD_MEM_REG =3D 37, > VHOST_USER_REM_MEM_REG =3D 38, > + VHOST_USER_SET_STATUS =3D 39, > + VHOST_USER_GET_STATUS =3D 40, > + VHOST_USER_MEM_DATA =3D 41, > VHOST_USER_MAX > } VhostUserRequest; > =20 > @@ -122,6 +125,7 @@ typedef enum VhostUserSlaveRequest { > VHOST_USER_SLAVE_FS_MAP =3D 6, > VHOST_USER_SLAVE_FS_UNMAP =3D 7, > VHOST_USER_SLAVE_FS_IO =3D 8, > + VHOST_USER_SLAVE_MEM_ACCESS =3D 9, > VHOST_USER_SLAVE_MAX > } VhostUserSlaveRequest; > =20 > @@ -220,6 +224,24 @@ typedef struct VhostUserInflight { > uint16_t queue_size; > } VhostUserInflight; > =20 > +/* For the flags field of VhostUserMemAccess and VhostUserMemReply */ > +#define VHOST_USER_MEM_FLAG_TO_MASTER (1u << 0) > +#define VHOST_USER_MEM_FLAG_FROM_MASTER (1u << 1) > +typedef struct VhostUserMemAccess { > + uint32_t id; /* Included in the reply */ > + uint32_t flags; Is VHOST_USER_MEM_FLAG_TO_MASTER | VHOST_USER_MEM_FLAG_FROM_MASTER valid? > + uint64_t addr; /* In the bus address of the device */ Please check the spec for preferred terminology. "bus address" isn't used in the spec, so there's probably another term for it. > + uint64_t len; /* In bytes */ > +} VhostUserMemAccess; > + > +typedef struct VhostUserMemReply { > + uint32_t id; /* From the request */ > + uint32_t flags; Are any flags defined? > + uint32_t err; /* 0 on success */ > + uint32_t align; Is this a reserved padding field? "align" is confusing because it could refer to some kind of memory alignment value. "reserved" or "padding" is clearer. > + uint64_t len; > +} VhostUserMemReply; > + > #if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__)) > # define VU_PACKED __attribute__((gcc_struct, packed)) > #else > @@ -248,6 +270,8 @@ typedef struct VhostUserMsg { > VhostUserVringArea area; > VhostUserInflight inflight; > VhostUserFSSlaveMsgMax fs_max; > + VhostUserMemAccess memaccess; > + VhostUserMemReply memreply; > } payload; > =20 > int fds[VHOST_MEMORY_BASELINE_NREGIONS]; > --=20 > 2.31.1 >=20 > --=20 > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK >=20 --qj6oTXXpImQHk+rE Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmDCPH0ACgkQnKSrs4Gr c8hrHggAxjTpWefcfpB+NyorglfeAAFFuAsMvL9eIBlXa2RbRGX8XZ9W76RkA3JN eNPZ4XTYnbGbS/Lp6xUt7rdWIZmLaH2V8b8HZHJCcXmwCONO97jiuoJ7KxZnE2jU fcBCP/Ldk3QkpIYo9K0zL9Rh9poJo71BckyMShTAn0FdlCEjSFiruYp+30CYGAr1 C8hV89aXyButGQuz26t8c32vGf2PS45+pNOJxLqhUvSNGsIxEv3wJReO4zm9hdTL 9/VxPxkNr8UUL4RggjXWZMIvfRbkoJnrEhlAfsaBqYtkAkpr/7t8P3fgxzN4uHfZ rhLOBfyzZ2M0v7oQDDwzvN1bZAGhGw== =XKaC -----END PGP SIGNATURE----- --qj6oTXXpImQHk+rE--