On Wed, Aug 22, 2018 at 9:54 PM Benjamin Herrenschmidt <benh@xxxxxxxxxxx> wrote:
>
>
> So we do need a different flush instruction for the page tables vs. the
> normal TLB pages.
Right. ARM wants it too. x86 is odd in that a regular "invlpg" already
invalidates all the internal tlb cache nodes.
So the "new world order" is exactly that patch that PeterZ sent you, that adds a
+ unsigned int freed_tables : 1;
to the 'struct mmu_gather', and then makes all those
pte/pmd/pud/p4d_free_tlb() functions set that bit.
So I'm referring to the email PeterZ sent you in this thread that said:
Nick, Will is already looking at using this to remove the synchronous
invalidation from __p*_free_tlb() for ARM, could you have a look to see
if PowerPC-radix could benefit from that too?
Basically, using a patch like the below, would give your tlb_flush()
information on if tables were removed or not.
then, in that model, you do *not* need to override these
pte/pmd/pud/p4d_free_tlb() macros at all (well, you *can* if you want
to, for doing games with the range modification, but let's sayt that
you don't need that right now).
So instead, when you get to the actual "tlb_flush(tlb)", you do
exactly that - flush the tlb. And the mmu_gather structure shows you
how much you need to flush. If you see that "freed_tables" is set,
then you know that you need to also do the special instruction to
flush the inner level caches. The range continues to show the page
range.
Linus
