From: Hugh Dickins <firstname.lastname@example.org> To: Andrea Arcangeli <email@example.com> Cc: Peter Xu <firstname.lastname@example.org>, Matthew Wilcox <email@example.com>, firstname.lastname@example.org, email@example.com, Andrew Morton <firstname.lastname@example.org>, Hugh Dickins <email@example.com>, Mike Rapoport <firstname.lastname@example.org>, David Hildenbrand <email@example.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.firstname.lastname@example.org> (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 22:47 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-11-30 23:06 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
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=alpine.LSU.email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --subject='Re: [PATCH v2] mm: Don'\''t fault around userfaultfd-registered regions on reads' \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).