OpenE2K
/
qemu-e2k
13
4
Fork 0
Code Issues 4 Pull Requests Projects 2 Releases Activity

vhost-user: document memory accesses 

The vhost-user protocol specification does not define "guest address"
and "user address".  It does not explain how to access memory given such
addresses.

This patch explains how memory access works, including the IOTLB.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2017-12-14 20:22:20 +00:00 committed by Michael S. Tsirkin
parent 7722b1a78a
commit c3d331d28f
1 changed files with 30 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
docs/interop/vhost-user.txt
View File

@ -66,11 +66,14 @@ Depending on the request type, payload can be:
Index: a 32-bit vring index
Flags: a 32-bit vring flags
Descriptor: a 64-bit user address of the vring descriptor table
Used: a 64-bit user address of the vring used ring
Available: a 64-bit user address of the vring available ring
Descriptor: a 64-bit ring address of the vring descriptor table
Used: a 64-bit ring address of the vring used ring
Available: a 64-bit ring address of the vring available ring
Log: a 64-bit guest address for logging
Note that a ring address is an IOVA if VIRTIO_F_IOMMU_PLATFORM has been
negotiated. Otherwise it is a user address.
* Memory regions description
---------------------------------------------------
| num regions | padding | region0 | ... | region7 |
@ -273,6 +276,30 @@ Once the source has finished migration, rings will be stopped by
the source. No further update must be done before rings are
restarted.
Memory access
-------------
The master sends a list of vhost memory regions to the slave using the
VHOST_USER_SET_MEM_TABLE message. Each region has two base addresses: a guest
address and a user address.
Messages contain guest addresses and/or user addresses to reference locations
within the shared memory. The mapping of these addresses works as follows.
User addresses map to the vhost memory region containing that user address.
When the VIRTIO_F_IOMMU_PLATFORM feature has not been negotiated:
* Guest addresses map to the vhost memory region containing that guest
address.
When the VIRTIO_F_IOMMU_PLATFORM feature has been negotiated:
* Guest addresses are also called I/O virtual addresses (IOVAs). They are
translated to user addresses via the IOTLB.
* The vhost memory region guest address is not used.
IOMMU support
-------------