integration with GA, GMB, and GSC.
It is very easy to catch, especially if you've never had it before.
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When VM=1, the protected-mode bit goes low and the Entry PLA selects real-mode entry points -- MOV ES, reg takes the one-line path. Meanwhile, CPL is hardwired to 3 whenever VM=1, so the V86 task always runs at the lowest privilege level, under full paging protection. The OS can use paging to virtualize the 8086's 1 MB address space, even simulating A20 address line wraparound by mapping pages to the same physical frames.
JIO_OK ("jump if I/O OK") tests whether CPL ≤ IOPL. The same check gates PUSHF, POPF, INT n, and IRET. The monitor then emulates each instruction as appropriate: maintaining a virtual interrupt flag per V86 task, reflecting software interrupts through the real-mode interrupt vector table, virtualizing I/O accesses, and so on.