16.5.2 Flushing Cached Data during PIO Operations

In some Windows NT platforms, the instruction and data caches in the processor exhibit cache coherency anomalies during PIO read operations.

To maintain data integrity during their read operations, NT drivers that use PIO must follow this guideline:

Call KeFlushIoBuffers at the end of each read operation.

For example, a driver making a PIO transfer from its device to system memory should call KeFlushIoBuffers at the end of each device transfer operation. As another example, a driver that reads a sequence of device registers into system memory should call KeFlushIoBuffers at the end of the sequence. Otherwise, such a driver might attempt to access data that is still in the processor's data cache, rather than in system memory, in some Windows NT platforms.

KeFlushIoBuffers does nothing if the processor can be relied on to maintain cache coherency, so calls to this support routine have almost no overhead in such a Windows NT platform.