Re: 2.4.19pre3aa2

Andrea Arcangeli
2002-03-14T16:14:17Z

On Thu, Mar 14, 2002 at 10:53:01AM -0500, Bill Davidsen wrote:
> On Thu, 14 Mar 2002, Dave Jones wrote:
>
> > On Thu, Mar 14, 2002 at 03:28:01AM +0100, Andrea Arcangeli wrote:
> > > Only in 2.4.19pre3aa2: 21_pte-highmem-f00f-1
> > >
> > > vmalloc called before smp_init was an hack, right way
> > > is to use fixmap. CONFIG_M686 doesn't mean much these
> > > days, but it's ok and probably most vendors will use it
> > > for the smp kernels, so it will save 4096 of the vmalloc space.
> > > I just didn't wanted to clobber the code with || CONFIG_K7 ||
> > > CONFIG_... | ... given all the other f00f stuff is also
> > > conditional only to M686 and probably nobody bothered to compile
> > > it out for my same reason
> >
> > Brian Gerst had a patch a few months back to introduce a CONFIG_F00F
> > if a relevant CONFIG_Mxxx was chosen[1]. It never got applied anywhere, but makes
> > more sense than the CONFIG_M686 we currently use.
> >
> > [1] 386/486/586. With addition of my Vendor choice menu, we could even further
> > narrow it down to Intel only.
>
> Since vendors (and consultants) like to build a single kernel for use on
> multiple machines, it would be nice if this could be done by some init
> code (released) and a module. I don't know what the overhead would be,
> perhaps the runtime code is so small it's not worth doing. Does that mean

Correct. I think the CONFIG option isn't worthwhile in the first place
and this is why I only left the CONFIG_M686 knowing most smp kernels are
compiled that way. 4096bytes of virtual vmallc space and some houndred
bytes of bytecode doesn't worth the config option. If something the
CONFIG_F00F would be more a documentation effort 8). But nevertheless if
somebody really cares, that still make sense and it doesn't hurt. At the
very least it is better than the current halfway broken CONFIG_M686.
But personally I'm not going to implement it and if I would really be
bothered by the halfway broken CONFIG_M686 I would drop it instead.

> it's not worth doing the option either? It certainly would seen desirable
> to check for the F00F bug and if the code to handle it was not present
> refuse to boot right away.
>
> The code actually looks so small as to be unworthy of an option, given
> that many people would set it off not knowing was it was much less whether
> they needed it. This is not like a missing FPU where you can do a graceful
> reject of the instructions, if you have the bug and not the fix you are
> vulnerable to sudden total failures, correct?
>
> --
> bill davidsen <davidsen@tmr.com>
> CTO, TMR Associates, Inc
> Doing interesting things with little computers since 1979.

Andrea