Re: x86 fpu: command-line parameters broken post-FPU-rewrite

From: Borislav Petkov
Date: Wed Dec 09 2015 - 14:14:31 EST

On Wed, Dec 09, 2015 at 09:32:10AM +0100, Ingo Molnar wrote:
> * Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> > Hey Ingo,
> >
> > We were starting to look at reenabling XSAVES support and tried to use the
> > 'noxsave' and 'noxsaves' kernel command-line options. The rewrite moved the FPU
> > initialization to before we even are parsing command-line options, even the
> > early_param()s.
> >
> > Do you have any preferences on how it gets fixed?
> >
> > The most obvious thing would be to just defer as much of the FPU setup as we can
> > until after parse_early_param() has happened. The only other think I can think
> > of doing would be to try to do some *really* early, simple, command-line parsing
> > to look for 'noxsave' and friends.
> >
> > Thoughts?
> Hm, so given that having the FPU operational is key to a functioning kernel (and
> other kernel subsystems may make use of FPU functionality), I'd rather bring
> option parsing earlier than change the FPU setup sequence. FPU setup should be
> done when we identify the CPU - not 'very late' as we used to.

We already have early cmdline parsing: arch/x86/lib/cmdline.c

See users for examples.


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