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Although kernel-mode drivers are forbidden to access pageable memory at a high IRQL or while holding a spin lock, such an action might not be noticed if the page has not actually been trimmed.
When Forcing IRQL Checking is enabled, Driver Verifier will provide extreme memory pressure on the selected driver. Whenever a driver being verified requests a spin lock, calls KeSynchronizeExecution, or raises the IRQL to DISPATCH_LEVEL or higher, all of the driver's pageable code and data (as well as system pageable pool, code, and data) are marked as trimmed. If the driver attempts to access any of this memory, Driver Verifier issues a bug check.
This memory pressure will not directly affect drivers that are not selected for verification, since other drivers' IRQL raises will not cause this action. However, when a driver that is being verified raises the IRQL, Driver Verifier trims pages that can be used by drivers that are not being verified. Thus errors by drivers that are not being verified might occasionally be caught when this option is active.
The number of IRQL raises, spin locks, and calls to KeSynchronizeExecution made by drivers being verified can be monitored. The number of pageable memory trims forced by Driver Verifier can also be monitored. These statistics can be displayed by the Driver Verifier Manager graphical interface, the verifier.exe command line, or in a log file. See Monitoring Global Counters for details.
The kernel debugger extension !verifier can also be used to monitor these statistics. It presents similar information to that of Driver Verifier Manager. In Windows XP and later, the !verifier 0x8 extension will display a log of recent IRQL changes made by drivers being verified. For information about debugger extensions, see Debugging Tools for NT-Based Operating Systems.
The Forcing IRQL Checking option can be activated by using the Driver Verifier Manager graphical interface or the verifier.exe command line. This activation will take effect after the next boot. See Selecting Driver Verifier Options for details.
This option can also be turned on and off without an intervening reboot. See Using Volatile Settings for details.
The Forcing IRQL Checking option is not used for graphics drivers. If selected, it has no effect.