This blocks an easy exploit of kernel bugs leading to dereference
of a NULL pointer on some architectures (eg i386).
The check can be disabled in various ways:
-by CPP definitions in machine/types.h (portmaster's choice)
-by a kernel config option USER_VA0_DISABLED_DEFAULT=0
-at runtime by sysctl vm.user_va0_disabled (cannot be cleared
at securelevel>0)
- Addresses the issue described in PR/38828.
- Some simplification in threading and sleepq subsystems.
- Eliminates pmap_collect() and, as a side note, allows pmap optimisations.
- Eliminates XS_CTL_DATA_ONSTACK in scsipi code.
- Avoids few scans on LWP list and thus potentially long holds of proc_lock.
- Cuts ~1.5k lines of code. Reduces amd64 kernel size by ~4k.
- Removes __SWAP_BROKEN cases.
Tested on x86, mips, acorn32 (thanks <mpumford>) and partly tested on
acorn26 (thanks to <bjh21>).
Discussed on <tech-kern>, reviewed by <ad>.
activity of other threads will perform the TLB flush for the processes using
emap as a side effect. To track that, global and per-CPU generation numbers
are used. This idea was suggested by Andrew Doran; various improvements to
it by me. Notes:
- For now, zero-copy on pipe is not yet enabled.
- TCP socket code would likely need more work.
- Additional UVM loaning improvements are needed.
Proposed on <tech-kern>, silence there.
Quickly reviewed by <ad>.
into modules. By and large this commit:
- shuffles header files and ifdefs
- splits code out where necessary to be modular
- adds module glue for each of the components
- adds/replaces hooks for things that can be installed at runtime
drochner