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by creshal 3860 days ago
> AMD dropped rings in their 64 bit architecture which Intel was forced to adopt, so they're becoming a historical curiosity.

Not quite. Hypervisors are operating in Ring -1, SMM is equivalent to another ring above that, and I can't find anything about AMD64 dropping Ring 1/2? Ring 0/3 at least are still in use.
2 comments
e12e 3860 days ago
AFAIK 64-bit linux has kernel in 0 and userspace in 3?

http://wiki.osdev.org/SYSENTER

http://www.x86-64.org/pipermail/discuss/2000-October/001068....

I tried looking at the latest 4.2 kernel tree - but the assembler/c-code that sets up and deals with sys-calls has been rather re-factored, so I'm not entirely adamant it's ring 0 and ring 3 for both 32bit and 64bit - but I think so? (From a quick glance, no sections stand out as calling out ring 3 explicitly when talking about returning to user-land -- granted I didn't do any searching over the code).

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hga 3860 days ago
I submit that "supervisor/user" isn't an implementation of "rings", plural (and it's got to predate Multics by a lot, but I can't quickly prove that), and that SMM is something entirely different. Hypervisors and there use really aren't comparable to Multics Rings.

A couple of minutes with Google only found hints that confirm my memory WRT to AMD64 and rings, and/or Intel not copying a segmentation feature added to later versions of AMD's chips.

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