linux-kernel - Re: [PATCH RFC 07/30] mm/swap: Introduce the idea of special swap ptes

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Date:   Tue, 19 Jan 2021 09:24:49 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Jerome Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Hugh Dickins <hughd@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Nadav Amit <nadav.amit@...il.com>
Subject: Re: [PATCH RFC 07/30] mm/swap: Introduce the idea of special swap
 ptes

On Mon, Jan 18, 2021 at 03:40:13PM -0400, Jason Gunthorpe wrote:
> Does the stuff in hmm.c need updating too?
> 
>         if (!pte_present(pte)) {
>                 swp_entry_t entry = pte_to_swp_entry(pte);

This idea should be cross-tree, so yes.. even if I'm not 100% sure whether HMM
would be a good candidate for file-backed uffd-wp, I agree we should also take
care of those.

I guess I managed to take care of all the is_swap_pte() callers but forget I
should also look for pte_to_swp_entry() users too, since sometimes pte_none()
and pte_present() is checked separately, so there're quite a few places that I
should have taken care of but got lost.  HMM is one of them.

Thanks for spotting this, Jason.  I'll coordinate in the next version.

-- 
Peter Xu