DOCUMENT:Q126349  03-NOV-1999  [win16ddk]
TITLE   :PRB: FastDisk BusMaster DMA Disk Devices Crashes When Paging
PRODUCT :Microsoft Windows Device Driver Kit
PROD/VER::3.1
OPER/SYS:
KEYWORDS:

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The information in this article applies to:

 - Microsoft Windows Device Development Kit (DDK) for Windows, version 3.1 
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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.

Additional query words: 3.10

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Keywords          :  
Technology        : kbAudDeveloper kbWin3xSearch kbWinDDKSearch kbWinDDK310
Version           : :3.1

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