Saturday, 26 April 2014

Process Directory Table Base and CR3 with Stop 0x101

This is a very simple error, and be can useful in providing a hint at which point the crash may have occurred. This has been explained by Scott Noone on this blog, but I wanted to write my own blog post about it and provide the data structure which he didn't mention. The error was found by Patrick in a Stop 0x101 bugcheck, and perfectly matches the context of the crash.

Looking at Parameter 4, we can see the Processor Index Number which has become hung. This is where the error message is located too. 

The highlighted address is the physical address stored within the CR3 Register. 

Using the !process extension on the same Processor Number Index, we can check the DirBase field to find the mismatch within the two address indicated in the error message. The DirBase is a physical address of the Process Directory Table Base.

The DirBase field is the field within structure formatted with !process, which contains the address of the Process Directory Table Base for the current process, and thus if the two addresses don't match, then WinDbg will produce that error string. It tends to be caused when a crash occurs during a context switch. You can find the same field under the _KPROCESS data structure:

 The Process Directory Table Base is private to each Process Address Space and is used with conjunction to the TLB Cache and TLB Flushing. It's all the virtual address pages which correspond to that process, and thus when a Context Switch occurs, then the Control Register can be changed to the address of the process and all the entries within the TLB Cache are flushed. Afterwards, when the new addresses have been loaded, each page translation will result in a complete page walk until all the TLB Cache Entries have been rebuilt. This is a expensive process, and thus some processor architectures will tag entries corresponding to certain processes, and then only flush the corresponding tags.


Process directory table base doesn't match CR3
Translation Lookside Buffer

Original Thread (Synsative) - BSOD(A clock interrupt was not recieved on a secondary processor...)

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