On Thu, Dec 16, 2021 at 06:45:07PM +1100, Alistair Popple wrote:

On Thursday, 16 December 2021 6:06:54 PM AEDT Peter Xu wrote:

[...]

quoted

I wondered how it could have worked - I thought e.g. pte_alloc_one() will
always return a pgtable page will all zero-filled, whose allocation should
require __GFP_ZERO anyway.  But then I quickly noticed that pte_alloc_one() is
per-arch too..  That explains, because per-arch can re-initialize the default
pte values.

Yes, I have wondered the same things before as well. It's all a little bit of
fun some of this stuff.

quoted

I thought this patch can greatly simplify things but I overlooked the
pte_none() check you mentioned.  So it seems I have no good choice but add that
flag back.

There's another alternative is we do pte_clear() on vmf->orig_pte as the new
way to initialize it.  I believe it should work too for s390 and xtensa.

Any preference?

I prefer the later approach (initialising to pte_clear) as it seems cleaner,
and pte_none(pte_clear()) is true for every architecture afaik.

Will do.

-- 
Peter Xu