Re: [PATCH 07/12] x86/tlb: use INVLPGB in flush_tlb_all

[Dave Hansen]

On 1/6/25 09:35, Rik van Riel wrote:
> On Mon, 2025-01-06 at 09:29 -0800, Dave Hansen wrote:
>> On 12/30/24 09:53, Rik van Riel wrote:
>>> --- a/arch/x86/mm/tlb.c
>>> +++ b/arch/x86/mm/tlb.c
>>> @@ -1074,6 +1074,12 @@ static void do_flush_tlb_all(void *info)
>>>  void flush_tlb_all(void)
>>>  {
>>>  	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
>>> +	if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
>>> +		guard(preempt)();
>>> +		invlpgb_flush_all();
>>> +		tlbsync();
>>> +		return;
>>> +	}
>>
>> After seeing a few of these, I'd really prefer that the preempt and
>> tlbsync() logic be hidden in the invlpgb_*() helper, or *a* helper at
>> least.
>>
>> This would be a lot easier on the eyes if it were something like:
>>
>> 	flushed = invlpgb_flush_all();
>> 	if (flushed)
>> 		return;
> 
> One issue here is that some of the invlpgb helpers
> are supposed to be asynchronous, because we can
> have multiple of those flushes pending simultaneously,
> and then wait for them to complete with a tlbsync.
> 
> How would we avoid the confusion between the two
> types (async vs sync) invlpgb helpers?

It could be done with naming. Either preface things with __ or give them
"sync" suffixes.

We could also do it with a calling convention:

	struct invlpgb_seq;

	start_invlpgb(&invlpgb_seq);
	invlpgb_flush_addr(&invlpgb_seq, start, end);
	end_invlpgb(&invlpgb_seq);

The things that can logically get done in sequence need to have the
start/end, and need to have the struct passed in. The ones that have the
internal sync don't have the argument.