From: Andrea Arcangeli <aarcange@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: Hugh Dickins <hughd@google.com>,
Matthew Wilcox <willy@infradead.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
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: Fri, 4 Dec 2020 13:12:56 -0500 [thread overview]
Message-ID: <X8p8KNJXD3aK9TkF@redhat.com> (raw)
In-Reply-To: <X8m2qv9h7+e79UjJ@redhat.com>
On Thu, Dec 03, 2020 at 11:10:18PM -0500, Andrea Arcangeli wrote:
> from the pte, one that cannot ever be set in any swp entry today. I
> assume it can't be _PAGE_SWP_UFFD_WP since that already can be set but
> you may want to verify it...
I thought more about the above, and I think the already existing
pte_swp_mkuffd_wp will just be enough without having to reserve an
extra bitflag if we encode it as a non migration entry.
The check:
if (!pte_present && !pte_none && pte_swp_uffd_wp && not_anonymous_vma && !is_migration_entry)
should be enough to disambiguate it. When setting it, it'd be enough
to set the pte to the value _PAGE_SWP_UFFD_WP.
Although if you prefer to check for:
if (!pte_present && !pte_none && swp_type == 1 && swp_offset == 0 && not_anonymous_vma && !is_migration_entry)
that would do as well.
It's up to you, just my preference is to reuse _PAGE_SWP_UFFD_WP since
it has already to exist, there are already all the pte_swp_*uffd*
methods available or uffd-wp cannot work.
Thanks,
Andrea
next prev parent reply other threads:[~2020-12-04 18:15 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
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 [this message]
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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