CVS commit: src/sys/arch/x86

["Andrius Varanavicius" <andvar%netbsd.org@localhost>]

Module Name:    src
Committed By:   andvar
Date:           Mon Jul  1 19:40:03 UTC 2024

Modified Files:
        src/sys/arch/x86/include: specialreg.h
        src/sys/arch/x86/x86: identcpu.c

Log Message:
Disable the VIA Alternate Instructions according the VIA documentation:
* C7 and above do not support ALTINST, do not check or attempt to disable them.
* For VIA C3 Nehemiah check extended feature flags for support and status,
do no attempt to disable when AIS is not supported or enabled.
* For pre-Nehemiah models explicitly disable, if they are in the range
of documented models, flags aren't present to check the status on these models.
Note: for pre-Nehemiah may be other functional side effects depdending
on the version and stepping.

Explicit disabling of ALTINST was introduced with rev. 1.84 following
the discovery of some VIA CPUs having these instructions enabled by default
leading to the potential backdoor (aka rosenbrindge).

Unfortunately, implementation used a wrong check (ACE supported flag),
which can be true for the later models, still supporting padlock features.
Setting ALTINST bit on those may have unexpected side effects like VIA C7 CPUID
instruction for temperature sensor not reporting correct value or
`cpuctl identify' not reporting certain CPU features. Similar side effects
can be observed even for Nehemiah models not supporting AIS instructions. This
change should limit possibility of such issues to only the pre-Nehemiah models,
not covered at all in the previous implementation.

Feature Control Register (FCR) macros were unified under one group and
consistent naming while implementing the change. Few comments updated as well.

patch reviewed by Riastradh@ (thank you)

need pullups to netbsd-9, 10.

PR kern/58370


To generate a diff of this commit:
cvs rdiff -u -r1.211 -r1.212 src/sys/arch/x86/include/specialreg.h
cvs rdiff -u -r1.129 -r1.130 src/sys/arch/x86/x86/identcpu.c

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