On Fri, 2023-02-10 at 00:50 +0100, Thomas Gleixner wrote:
> On Thu, Feb 09 2023 at 20:32, Usama Arif wrote:
> > On 09/02/2023 18:31, Thomas Gleixner wrote:
> > > > first_cpu = cpumask_first(cpu_online_mask);
> > > > smp_call_function_single(first_cpu, mtrr_save_fixed_ranges, NULL, 1);
> > >
> > > So why is this relevant after the initial bringup? The BP MTRRs have
> > > been saved already above, no?
> > >
> >
> > I will let David confirm if this is correct and why he did it, but this
> > is what I thought while reviewing before posting v4:
> >
> > - At initial boot (system_state < SYSTEM_RUNNING), when mtrr_save_state
> > is called in do_cpu_up at roughly the same time so MTRR is going to be
> > the same, we can just save it once and then reuse for other secondary
> > cores as it wouldn't have changed for the rest of the do_cpu_up calls.
> >
> > - When the system is running and you offline and then online a CPU, you
> > want to make sure that hotplugged CPU gets the current MTRR (which might
> > have changed since boot?), incase the MTRR has changed after the system
> > has been booted, you save the MTRR of the first online CPU. When the
> > hotplugged CPU runs its initialisation code, its fixed-range MTRRs will
> > be updated with the newly saved fixed-range MTRRs.
>
> I knew that already :) But seriously:
>
> If the MTRRs are changed post boot then the cached values want to be
> updated too.
They are, aren't they? The only way we come out of mtrr_save_state()
without calling mtrr_save_fixed_ranges() — either directly or via
smp_call_function_single() — is if they've already been saved once
*and* system_state < SYSTEM_RUNNING.
I suppose we could make that clearer by moving the definition of the
mtrr_saved flags inside the if (system_state < SYSTEM_RUNNING) block?
@@ -721,11 +721,20 @@ void __init mtrr_bp_init(void)
*/
void mtrr_save_state(void)
{
int first_cpu;
if (!mtrr_enabled())
return;
+ if (system_state < SYSTEM_RUNNING) {
+ static bool mtrr_saved;
+ if (!mtrr_saved) {
+ mtrr_save_fixed_ranges(NULL);
+ mtrr_saved = true;
+ }
+ return;
+ }
+
first_cpu = cpumask_first(cpu_online_mask);
smp_call_function_single(first_cpu, mtrr_save_fixed_ranges, NULL, 1);
}
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