From: Hugh Dickins <hughd@google.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Peter Xu <peterx@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v2] mm: Don't fault around userfaultfd-registered regions on reads
Date: Wed, 2 Dec 2020 14:37:33 -0800 (PST) [thread overview]
Message-ID: <alpine.LSU.2.11.2012021410260.4989@eggly.anvils> (raw)
In-Reply-To: <X8bZk3jTGU8QyJWc@redhat.com>
On Tue, 1 Dec 2020, Andrea Arcangeli wrote:
>
> Any suggestions on how to have the per-vaddr per-mm _PAGE_UFFD_WP bit
> survive the pte invalidates in a way that remains associated to a
> certain vaddr in a single mm (so it can shoot itself in the foot if it
> wants, but it can't interfere with all other mm sharing the shmem
> file) would be welcome...
I think it has to be a new variety of swap-like non_swap_entry() pte,
see include/linux/swapops.h. Anything else would be more troublesome.
Search for non_swap_entry and for migration_entry, to find places that
might need to learn about this new variety.
IIUC you only need a single value, no need to carve out another whole
swp_type: could probably be swp_offset 0 of any swp_type other than 0.
Note that fork's copy_page_range() does not "copy ptes where a page
fault will fill them correctly", so would in effect put a pte_none
into the child where the parent has this uffd_wp entry. I don't know
anything about uffd versus fork, whether that would pose a problem.
Hugh
next prev parent reply other threads:[~2020-12-02 22:37 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-30 23:06 [PATCH v2] mm: Don't fault around userfaultfd-registered regions on reads Peter Xu
2020-12-01 9:30 ` David Hildenbrand
2020-12-01 12:59 ` Matthew Wilcox
2020-12-01 22:30 ` Peter Xu
2020-12-02 0:02 ` Andrea Arcangeli
2020-12-02 22:37 ` Hugh Dickins [this message]
2020-12-02 23:41 ` Peter Xu
2020-12-03 5:36 ` Hugh Dickins
2020-12-03 18:02 ` Peter Xu
2020-12-03 19:44 ` Andrea Arcangeli
2020-12-04 2:30 ` Peter Xu
2020-12-04 4:10 ` Andrea Arcangeli
2020-12-04 5:59 ` Hugh Dickins
2020-12-04 16:50 ` Peter Xu
2020-12-04 18:12 ` Andrea Arcangeli
2020-12-04 19:23 ` Peter Xu
2020-12-04 19:37 ` Andrea Arcangeli
2020-12-04 20:21 ` Peter Xu
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