Operating Systems 2019W Lecture 22

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The video for the lecture given on April 3, 2019 is now available: Part 1, Part 2.


Lecture 22

Atomic operations
hardware virtualization

Atomic operations

atom means "indivisible" in the original greek?

an atomic operation is thus indivisible
 - it completes or it doesn't happen

a transaction is a simulation of an atomic operation
 - if parts of the transaction fail, you undo everything

Hardware virtualization
want to run multiple operating systems on one system
 - so multiple kernels

But kernels are special.  They expect access to:
 - hardware-level interrupts
 - run in supervisor mode
 - devices
 - page tables
 - software interrupts (system call invocations)

Two strategies:
 - fake it (emulation)
    - to make it fast, just emulate the privileged operations
    - original strategy of vmware on x86

 - hardware virtualizes resources
   - hypervisor mode over supervisor mode (ring -1)
   - shadow page tables (virtualization of page tables)
   - devices are faked or do their own virtualization