Peter Xu 2ff559f31a Revert "userfaultfd: don't fail on unrecognized features"
This is a proposal to revert commit 914eedcb9b.

I found this when writing a simple UFFDIO_API test to be the first unit
test in this set.  Two things breaks with the commit:

  - UFFDIO_API check was lost and missing.  According to man page, the
  kernel should reject ioctl(UFFDIO_API) if uffdio_api.api != 0xaa.  This
  check is needed if the api version will be extended in the future, or
  user app won't be able to identify which is a new kernel.

  - Feature flags checks were removed, which means UFFDIO_API with a
  feature that does not exist will also succeed.  According to the man
  page, we should (and it makes sense) to reject ioctl(UFFDIO_API) if
  unknown features passed in.

Link: https://lore.kernel.org/r/20220722201513.1624158-1-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20230412163922.327282-2-peterx@redhat.com
Fixes: 914eedcb9b ("userfaultfd: don't fail on unrecognized features")
Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Zach O'Keefe <zokeefe@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-04-16 10:41:26 -07:00
2022-09-28 09:02:20 +02:00
2023-03-26 14:40:20 -07:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
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