On Thursday, 16 December 2021 6:06:54 PM AEDT Peter Xu wrote: [...] > 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. > 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. > Thanks, > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > This change prepares us to be able to call do_fault() on !none ptes. For > > > > > > example, we should allow that to happen for pte marker so that we can restore > > > > > > information out of the pte markers. > > > > > > > > > > > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > > > > > > --- > > > > > > mm/memory.c | 2 +- > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/mm/memory.c b/mm/memory.c > > > > > > index 04662b010005..d5966d9e24c3 100644 > > > > > > --- a/mm/memory.c > > > > > > +++ b/mm/memory.c > > > > > > @@ -4052,7 +4052,7 @@ vm_fault_t finish_fault(struct vm_fault *vmf) > > > > > > vmf->address, &vmf->ptl); > > > > > > ret = 0; > > > > > > /* Re-check under ptl */ > > > > > > - if (likely(pte_none(*vmf->pte))) > > > > > > + if (likely(pte_same(*vmf->pte, vmf->orig_pte))) > > > > > > do_set_pte(vmf, page, vmf->address); > > > > > > else > > > > > > ret = VM_FAULT_NOPAGE; > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
