Compatibility: DPMI 0.9+
Expects: AX    0900H
                                                                  
Returns: CF    NC (clear; always successful)
AL    previous setting: 00H = virtual interrupts were disabled
01H = virtual interrupts were enabled
                                                                  
Info: Disables the virtual interrupt flag and returns the previous
state of that flag.

AH is not modified by the call, so you can return to the previous
state immediately by calling INT 31H.

If you don't need to know the previous state, you may simply use
the CLI opcode.

See Also: DPMI API
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INT 31H 0900H: Query and Disable Virtual Interrupt State