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+@node pcsys_ivshmem
+@section Inter-VM Shared Memory device
+
+On Linux hosts, a shared memory device is available.  The basic syntax
+is:
+
+@example
+@value{qemu_system_x86} -device ivshmem-plain,memdev=@var{hostmem}
+@end example
+
+where @var{hostmem} names a host memory backend.  For a POSIX shared
+memory backend, use something like
+
+@example
+-object memory-backend-file,size=1M,share,mem-path=/dev/shm/ivshmem,id=@var{hostmem}
+@end example
+
+If desired, interrupts can be sent between guest VMs accessing the same shared
+memory region.  Interrupt support requires using a shared memory server and
+using a chardev socket to connect to it.  The code for the shared memory server
+is qemu.git/contrib/ivshmem-server.  An example syntax when using the shared
+memory server is:
+
+@example
+# First start the ivshmem server once and for all
+ivshmem-server -p @var{pidfile} -S @var{path} -m @var{shm-name} -l @var{shm-size} -n @var{vectors}
+
+# Then start your qemu instances with matching arguments
+@value{qemu_system_x86} -device ivshmem-doorbell,vectors=@var{vectors},chardev=@var{id}
+                 -chardev socket,path=@var{path},id=@var{id}
+@end example
+
+When using the server, the guest will be assigned a VM ID (>=0) that allows guests
+using the same server to communicate via interrupts.  Guests can read their
+VM ID from a device register (see ivshmem-spec.txt).
+
+@subsection Migration with ivshmem
+
+With device property @option{master=on}, the guest will copy the shared
+memory on migration to the destination host.  With @option{master=off},
+the guest will not be able to migrate with the device attached.  In the
+latter case, the device should be detached and then reattached after
+migration using the PCI hotplug support.
+
+At most one of the devices sharing the same memory can be master.  The
+master must complete migration before you plug back the other devices.
+
+@subsection ivshmem and hugepages
+
+Instead of specifying the <shm size> using POSIX shm, you may specify
+a memory backend that has hugepage support:
+
+@example
+@value{qemu_system_x86} -object memory-backend-file,size=1G,mem-path=/dev/hugepages/my-shmem-file,share,id=mb1
+                 -device ivshmem-plain,memdev=mb1
+@end example
+
+ivshmem-server also supports hugepages mount points with the
+@option{-m} memory path argument.
+