Re: [PATCH v1 02/47] x86: mtrr: generalize run time disabling of MTRR

Luis R. Rodriguez
2015-04-03T01:09:08Z

On Thu, Apr 02, 2015 at 05:52:16PM -0600, Toshi Kani wrote:
> On Thu, 2015-04-02 at 23:49 +0200, Luis R. Rodriguez wrote:
> > On Sat, Mar 28, 2015 at 12:56:30AM +0100, Luis R. Rodriguez wrote:
> > > On Fri, Mar 27, 2015 at 02:40:17PM -0600, Toshi Kani wrote:
> > > > On Fri, 2015-03-20 at 16:17 -0700, Luis R. Rodriguez wrote:
> > > > :
> > > > > @@ -734,6 +742,7 @@ void __init mtrr_bp_init(void)
> > > > > }
> > > > >
> > > > > if (mtrr_if) {
> > > > > + mtrr_enabled = true;
> > > > > set_num_var_ranges();
> > > > > init_table();
> > > > > if (use_intel()) {
> > > > get_mtrr_state();
> > > >
> > > > After setting mtrr_enabled to true, get_mtrr_state() reads
> > > > MSR_MTRRdefType and sets 'mtrr_state.enabled', which also indicates if
> > > > MTRRs are enabled or not on the system. So, potentially, we could have
> > > > a case that mtrr_enabled is set to true, but mtrr_state.enabled is set
> > > > to disabled when MTRRs are disabled by BIOS.
> > >
> > > Thanks for the review, in this case then we should update mtrr_enabled to false.
> > >
> > > > ps.
> > > > I recently cleaned up this part of the MTRR code in the patch below,
> > > > which is currently available in the -mm & -next trees.
> > > > https://lkml.org/lkml/2015/3/24/1063
> > >
> > > Great I will rebase and work with that and try to address this
> > > consideration you have raised.
> >
> > OK I'll mesh in this change as well in my next respin:
> >
> > diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
> > index a83f27a..ecf7cb9 100644
> > --- a/arch/x86/kernel/cpu/mtrr/generic.c
> > +++ b/arch/x86/kernel/cpu/mtrr/generic.c
> > @@ -438,7 +438,7 @@ static void __init print_mtrr_state(void)
> > }
> >
> > /* Grab all of the MTRR state for this CPU into *state */
> > -void __init get_mtrr_state(void)
> > +bool __init get_mtrr_state(void)
> > {
> > struct mtrr_var_range *vrs;
> > unsigned long flags;
> > @@ -482,6 +482,8 @@ void __init get_mtrr_state(void)
> >
> > post_set();
> > local_irq_restore(flags);
> > +
> > + return !!mtrr_state.enabled;
>
> This should be:
> return mtrr_state.enabled & MTRR_STATE_MTRR_ENABLED;
>
> because the MTRR_STATE_MTRR_FIXED_ENABLED flag is ignored when the
> MTRR_STATE_MTRR_ENABLED flag is clear.

Thanks, I've used

return !!(mtrr_state.enabled & MTRR_STATE_MTRR_ENABLED);

Amended.

Luis