XvioCreateRingBuffer function

Creates a ring buffer for passing large amounts of data between partitions. Interestingly, it seems to be used as an auxiliary XvioPostMessage in some cases, though the reason for this is unknown.

Syntax

C++

NTSTATUS XvioCreateRingBuffer(
    uint32_t ContextId,
    uint64_t TargetPartition,
    uint16_t Unk1,
    uint32_t ReceivePageCount,
    uint32_t SendPageCount,
    PXVIO_RING_BUFFER RingBuffer
);

Parameters

uint32_t ContextId
The Context ID to communicate to on the remote partition.

uint64_t TargetPartition
Target partition for the ring buffer to be shared with. See partition identifiers for a list of partitions and their corresponding IDs.

uint16_t Unk1
Not sure what this is, seems important though. Perhaps allocation type?

uint32_t ReceivePageCount
Amount of pages, used for reading data, to be allocated to the ring buffer.

uint32_t SendPageCount
Amount of pages, used for writing data, to be allocated to the ring buffer.

PXVIO_RING_BUFFER RingBuffer
Pointer to an XVIO_RING_BUFFER structure, used for output.

Return value

Returns a generic NTSTATUS value.

Under the microscope

Put simply, XvioCreateRingBuffer allocates a user-specified amount of contiguous physical pages. The guest physical address of these pages are then posted to HostOS, amongst other data, with the message code 0x5 - which I've chosen to name RingBufferAction as the same code is used when destroying a ring buffer. The local partition then waits for the Ring Buffer's synchronization event to be signalled (presumably by HostOS) before returning the Ring Buffer Context to the caller.

Research into how HostOS handles a RingBufferAction is planned, I've just yet to get around to it :)

Authors: Harry Woolford