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(multiboot.info)I/O restriction technique

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I/O restriction technique
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   This first step may be unnecessary, but first create copy-on-write
mappings for the device drivers writing into PC RAM. Keep the original
copies for the "clean BIOS virtual machine" to be created later.

   For each device driver brought online, determine which BIOS devices
become inaccessible by:

  1. Create a "clean BIOS virtual machine".

  2. Set the I/O permission map for the I/O area claimed by the device
     driver to no permissions (neither read nor write).

  3. Access each device.

  4. Record which devices succeed, and those which try to access the
     "restricted" I/O areas (hopefully, this will be an "xor"
     situation).

   For each device driver, given how many of the BIOS devices were
subsumed by it (there should be no gaps in this list), it should be easy
to determine which devices on the controller these are.

   In general, you have at most 2 disks from each controller given BIOS
numbers, but they pretty much always count from the lowest logically
numbered devices on the controller.