PRB: FastDisk BusMaster DMA Disk Devices Crashes When Paging

• Microsoft Windows Device Drvier Development Kit (DDK) for Windows version 3.1

SYMPTOMS

The FastDisk device driver crashes once paging starts to occur on BusMastering DMA disk controller.

CAUSE

The snooper hardware on the i486 and Pentium processors does not properly detect when a BusMaster device has written to pages in memory. Therefore, the dirty bit in these pages does not get set. The PAGESWAP device in Windows enhanced mode relies on the dirty bit for paging. Therefore, when a paging request is made, the pages do not get updated, so new code or data is not paged in. This causes any application that was paging in code or data to crash on invalid data in the regions that should have been paged in.

RESOLUTION

In the fastdisk driver's BDD_Hw_Int_Proc, which is called when the command completes, the fastdisk driver should touch all pages that were updated by the BusMaster DMA by doing a DWORD READ/WRITE BACK on the first DWORD in each page. This will cause the cache to set the dirty bit in each of the affected pages manually, and cause the PAGESWAP device to function correctly.