[Bug 219399] System panics after several hours of 14-threads-compilation orgies using poudriere on AMD Ryzen...

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=219399

--- Comment #213 from Nils Beyer <nbe at renzel.net> ---
(In reply to Nils Beyer from comment #212)

more statements:
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I'm new to this myself (I work on the GPU SW side) but AFAICS there are at
least three different CPU families (1 from AMD) over the last decade which
require special treatment, basically making sure that no code gets executed
near the end of canonical user address space. The top of user process address
space is the dividing line between the least privileged code and the
touch-it-and-die non-canonical address space.

Over time it seems that more "safe area" is required - presumably because each
new CPU generation pre-fetches further ahead than the last one. In a sense
Linux (and Windows I believe) got lucky by reserving a full guard page while
BSD allocated a smaller guard area. As a result BSD has had to bump the guard
area (to a full page) while other OSes did not.
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