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.
*/
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:
> 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);
> }
