On Thu, Feb 22, 2024 at 08:48:17AM -0800, Dave Hansen wrote:
> On 1/26/24 00:06, Yosry Ahmed wrote:
> > +/*
> > + * The "prev" argument passed by the caller does not always match CR3. For
> > + * example, the scheduler passes in active_mm when switching from lazy TLB mode
> > + * to normal mode, but switch_mm_irqs_off() can be called from x86 code without
> > + * updating active_mm. Use cpu_tlbstate.loaded_mm instead.
> > + */
> > +void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next,
> > struct task_struct *tsk)
>
> One nit here: It's not obvious that "unused" is 'the "prev" argument'.
>
> Would something like this be more clear?
>
> /*
> * This optimizes when not actually switching mm's. Some architectures
> * use the 'unused' argument for this optimization, but x86 must use
> * 'cpu_tlbstate.loaded_mm' instead because it does not always keep
> * ->active_mm up to date.
> */
Yes, this is more clear, thanks! However, Andrew already merged that
patch into mm-stable, so it cannot be amended. I can send a separate
patch to rewrite the comment tho if you'd like, WDYT?
>
> Also, I think it might be useful to have the rule that arch/x86 code
> _always_ calls switch_mm_irqs_off() with the first argument (the
> newly-named 'unused') set to NULL. I think there's only one site:
Agreed. I can also send a separate patch for this. Thanks!
>
> > void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> > struct task_struct *tsk)
> > {
> > unsigned long flags;
> >
> > local_irq_save(flags);
> > switch_mm_irqs_off(prev, next, tsk);
> > local_irq_restore(flags);
> > }
>
