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[PATCH V3 2/2] docs: vhost-user: Add Xen specific memory mapping support
From: |
Viresh Kumar |
Subject: |
[PATCH V3 2/2] docs: vhost-user: Add Xen specific memory mapping support |
Date: |
Thu, 9 Mar 2023 14:21:01 +0530 |
The current model of memory mapping at the back-end works fine where a
standard call to mmap() (for the respective file descriptor) is enough
before the front-end can start accessing the guest memory.
There are other complex cases though where the back-end needs more
information and simple mmap() isn't enough. For example Xen, a type-1
hypervisor, currently supports memory mapping via two different methods,
foreign-mapping (via /dev/privcmd) and grant-dev (via /dev/gntdev). In
both these cases, the back-end needs to call mmap() and ioctl(), with
extra information like the Xen domain-id of the guest whose memory we
are trying to map.
Add a new protocol feature, 'VHOST_USER_PROTOCOL_F_XEN_MMAP', which lets
the back-end know about the additional memory mapping requirements.
When this feature is negotiated, the front-end will send the additional
information within the memory regions themselves.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
docs/interop/vhost-user.rst | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 1720d681264d..5a070adbc1aa 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -145,6 +145,26 @@ Memory region description
:mmap offset: 64-bit offset where region starts in the mapped memory
+When the ``VHOST_USER_PROTOCOL_F_XEN_MMAP`` protocol feature has been
+successfully negotiated, the memory region description contains two extra
+fields at the end.
+
++---------------+------+--------------+-------------+----------------+-------+
+| guest address | size | user address | mmap offset | xen mmap flags | domid |
++---------------+------+--------------+-------------+----------------+-------+
+
+:xen mmap flags: 32-bit bit field
+
+- Bit 0 is set for Xen foreign memory mapping.
+- Bit 1 is set for Xen grant memory mapping.
+- Bit 8 is set if the memory region can not be mapped in advance, and memory
+ areas within this region must be mapped / unmapped only when required by the
+ back-end. The back-end shouldn't try to map the entire region at once, as the
+ front-end may not allow it. The back-end should rather map only the required
+ amount of memory at once and unmap it after it is used.
+
+:domid: a 32-bit Xen hypervisor specific domain id.
+
Single memory region description
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -864,6 +884,7 @@ Protocol features
#define VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS 14
#define VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS 15
#define VHOST_USER_PROTOCOL_F_STATUS 16
+ #define VHOST_USER_PROTOCOL_F_XEN_MMAP 17
Front-end message types
-----------------------
--
2.31.1.272.g89b43f80a514