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

[Toshi Kani <toshi.kani@xxxxxx>]

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,
-Toshi




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