Re: [PATCH 10/14] prctl.2: Add PR_SPEC_INDIRECT_BRANCH for SPECULATION_CTRL prctls

[Dave Martin <Dave.Martin@arm.com>]

On Wed, May 13, 2020 at 01:21:12PM +0200, Michael Kerrisk (man-pages) wrote:
> Hello Dave,
> 
> On 5/12/20 6:36 PM, Dave Martin wrote:
> > Add the PR_SPEC_INDIRECT_BRANCH "misfeature" added in Linux 4.20
> > for PR_SET_SPECULATION_CTRL and PR_GET_SPECULATION_CTRL.
> > 
> > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> > Cc: Tim Chen <tim.c.chen@linux.intel.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> 
> Thanks. Patch applied, but not yet pushed while I wait to see if any
> Review/Ack arrives.
> 
> Also, could you please check the tweaks I note below.
> 
> > ---
> >  man2/prctl.2 | 24 ++++++++++++++++++------
> >  1 file changed, 18 insertions(+), 6 deletions(-)
> > 
> > diff --git a/man2/prctl.2 b/man2/prctl.2
> > index e8eaf95..66417cf 100644
> > --- a/man2/prctl.2
> > +++ b/man2/prctl.2
> > @@ -1213,11 +1213,20 @@ arguments must be specified as 0; otherwise the call fails with the error
> >  .\" commit 356e4bfff2c5489e016fdb925adbf12a1e3950ee
> >  Sets the state of the speculation misfeature specified in
> >  .IR arg2 .
> > -Currently, the only permitted value for this argument is
> > +Currently, this argument must be one of:
> > +.RS
> > +.TP
> >  .B PR_SPEC_STORE_BYPASS
> > -(otherwise the call fails with the error
> > +speculative store bypass control, or
> 
> s/speculative/enable speculative/
> 
> > +.\" commit 9137bb27e60e554dab694eafa4cca241fa3a694f
> > +.TP
> > +.BR PR_SPEC_INDIRECT_BRANCH " (since Linux 4.20)"
> > +indirect branch speculation control.
> 
> s/indirect/enable indirect/

That doesn't seem quite right.

arg2 just identifies what behaviour to configure.
It's arg3 that says whether to disable / enable it or whatever.


While editing this I did wonder whether the "control" was helpful.
Maybe just dropping that word from these entries would help.

[...]

Cheers
---Dave