CVS commit: src/sys/arch

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Fri May  8 00:49:43 UTC 2020

Modified Files:
        src/sys/arch/amd64/amd64: machdep.c
        src/sys/arch/x86/include: pmap.h
        src/sys/arch/x86/x86: pmap.c

Log Message:
Factor randomization out of slotspace_rand.

slotspace_rand becomes deterministic; the randomization moves into
the callers instead.  Why?

There are two callers of slotspace_rand:

- x86/pmap.c pmap_bootstrap
- amd64/amd64.c init_slotspace

When the randomization was introduced, it used an x86-only
`cpu_earlyrng' abstraction that would hash rdseed/rdrand and rdtsc
output together.  Except init_slotspace ran before cpu_probe, so
cpu_feature was not yet filled out, so during init_slotspace, the
only randomization was rdtsc.

In the course of the recent entropy overhaul, I replaced cpu_earlyrng
by entropy_extract, and moved cpu_init_rng much earlier -- but still
after cpu_probe -- in order to reduce the number of abstractions
lying around and the number of copies of rdrand/rdseed logic.  In so
doing I added some annoying complication (see curcpu_available) to
kern_entropy.c to make it work early enough for init_slotspace, and
dropped the rdtsc.

For pmap_bootstrap that didn't substantively change anything.  But
for init_slotspace, it removed the only randomization.  To mitigate
this, this commit pulls the randomization out of slotspace_rand into
pmap_bootstrap and init_slotspace, so that

(a) init_slotspace can use rdtsc and a little private entropy pool in
    order to restore the prior (weak) randomization it had, and

(b) pmap_bootstrap, which runs a little bit later, can continue to
    use entropy_extract normally and get rdrand/rdseed too.

A subsequent commit will move cpu_init_rng just a wee bit later,
after cpu_init_msrs, so the kern_entropy.c complications can go away.
Perhaps someone else more wizardly with x86 can find a way to make
init_slotspace run a little later too, after cpu_probe and after
cpu_init_msrs and after cpu_rng_init, but I am not that wizardly.


To generate a diff of this commit:
cvs rdiff -u -r1.352 -r1.353 src/sys/arch/amd64/amd64/machdep.c
cvs rdiff -u -r1.119 -r1.120 src/sys/arch/x86/include/pmap.h
cvs rdiff -u -r1.388 -r1.389 src/sys/arch/x86/x86/pmap.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.