Re: [patch 51/60] x86/mm: Allow flushing for future ASID switches

[Andy Lutomirski]

On Mon, Dec 4, 2017 at 2:34 PM, Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> On 12/04/2017 02:22 PM, Andy Lutomirski wrote:
>>> +
>>> +       this_cpu_write(cpu_tlbstate.invalidate_other, true);
>>
>> Why do we need this extra variable instead of just looping over all
>> other ASIDs and invalidating them?  It would be something like:
>>
>>         for (i = 1; i < TLB_NR_DYN_ASIDS; i++) {
>>                 if (i != this_cpu_read(cpu_tlbstate.loaded_mm_asid))
>>                        this_cpu_write(cpu_tlbstate.ctxs[i].ctx_id, 0);
>>         }
>
> We have loops like this:
>
>         for (addr = start; addr < end; addr += PAGE_SIZE)
>                 flush_tlb_single();

Couldn't we just make those looks more intelligent:

for (...)
  flush_tlb_kernelmode_single(...);

if (kpti)
  invalidate_asid_other();

(Isn't there only one such look now, in flush_tlb_func_common()?)

--Andy