Re: [tip: x86/mm] x86/mm/tlb: Update mm_cpumask lazily

[Peter Zijlstra]

On Tue, Nov 19, 2024 at 11:27:35AM -0000, tip-bot2 for Rik van Riel wrote:
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index d17518c..8b66a55 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -1825,11 +1825,18 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
>  	return temp_state;
>  }
>  
> +__ro_after_init struct mm_struct *poking_mm;
> +__ro_after_init unsigned long poking_addr;
> +
>  static inline void unuse_temporary_mm(temp_mm_state_t prev_state)
>  {
>  	lockdep_assert_irqs_disabled();
> +
>  	switch_mm_irqs_off(NULL, prev_state.mm, current);
>  
> +	/* Clear the cpumask, to indicate no TLB flushing is needed anywhere */
> +	cpumask_clear_cpu(raw_smp_processor_id(), mm_cpumask(poking_mm));

Oh bugger, this is really unfortunate.

Let me try and fix this.