svn commit: r328625 - in head/sys: amd64/amd64 amd64/ia32 amd64/include dev/cpuctl i386/i386 x86/include x86/x86

[Konstantin Belousov]

On Wed, Jan 31, 2018 at 02:56:24PM +0000, Bjoern A. Zeeb wrote:
> On 31 Jan 2018, at 14:36, Konstantin Belousov wrote:
> 
> > Author: kib
> > Date: Wed Jan 31 14:36:27 2018
> > New Revision: 328625
> > URL: https://svnweb.freebsd.org/changeset/base/328625
> >
> > Log:
> >   IBRS support, AKA Spectre hardware mitigation.
> 
> >   For existing processors, you need a microcode update which adds IBRS
> >   CPU features, and to manually enable it by setting the 
> > tunable/sysctl
> >   hw.ibrs_disable to 0.  Current status can be checked in sysctl
> >   hw.ibrs_active.  The mitigation might be inactive if the CPU feature
> 
> Can you change the tunable/sysctl to hw.ibrs_enable[d] (and toggle the 
> default setting along).
This is done consistently with the hw.clflush_disable.
Anyway, the intent is that the knob will be used for disabling,
since defaults are going to be changed in the near future.

> I find it highly confusing to have two different sysctls ???disable??? 
> and ???active??? and a lot
> of people (and cultures) have trouble with the double negative.
> Also the ???enable[d]??? variant seems to be pre-dominant in the kernel.
> 
> Also can we spell IBRS in the sysctl description as ???Indirect Branch 
> Restricted Speculation (IBRS)????
Will do in half a hour.