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

["Luis R. Rodriguez" <mcgrof@xxxxxxxx>]

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;
 }
 
 /* Some BIOS's are messed up and don't set all MTRRs the same! */
diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index ea5f363..f96195e 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -734,22 +742,25 @@ void __init mtrr_bp_init(void)
        }
 
        if (mtrr_if) {
+               mtrr_enabled = true;
                set_num_var_ranges();
                init_table();
                if (use_intel()) {
-                       get_mtrr_state();
+                       /* BIOS may override */
+                       mtrr_enabled = get_mtrr_state();
 
                        if (mtrr_cleanup(phys_addr)) {
                                changed_by_mtrr_cleanup = 1;
@@ -745,11 +755,14 @@ void __init mtrr_bp_init(void)
                        }
                }
        }
+
+       if (!mtrr_enabled)
+               pr_info("mtrr: system does not support MTRR\n");
 }
 

diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.h b/arch/x86/kernel/cpu/mtrr/mtrr.h
index df5e41f..951884d 100644
--- a/arch/x86/kernel/cpu/mtrr/mtrr.h
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.h
@@ -51,7 +51,7 @@ void set_mtrr_prepare_save(struct set_mtrr_context *ctxt);
 
 void fill_mtrr_var_range(unsigned int index,
                u32 base_lo, u32 base_hi, u32 mask_lo, u32 mask_hi);
-void get_mtrr_state(void);
+bool get_mtrr_state(void);
 
 extern void set_mtrr_ops(const struct mtrr_ops *ops);
 

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