Re: [PATCH v14 05/13] x86/mm: use INVLPGB in flush_tlb_all

[Dave Hansen <dave.hansen@intel.com>]

On 2/25/25 19:00, Rik van Riel wrote:
>  void flush_tlb_all(void)
>  {
>  	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
> +
> +	/* First try (faster) hardware-assisted TLB invalidation. */
> +	if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
> +		guard(preempt)();
> +		invlpgb_flush_all();
> +		return;
> +	}

We haven't talked at all about the locking rules for
invlpgb_flush_all(). It was used once in this series without any
explicit preempt twiddling. I assume that was because it was used in a
path where preempt is disabled.

If it does need a universal rule about preempt, can we please add an:

	lockdep_assert_preemption_disabled()

along with a comment about why it needs preempt disabled?

Also, the previous code did:

	if (cpu_feature_enabled(X86_FEATURE_INVLPGB))
		invlpgb_foo();
	else
		old_foo();

Is there a reason to break with that pattern? It would be nice to be
consistent.