Re: [PATCH 06/10] ioctl_userfaultfd.2: describe missing UFFDIO_API feature flags

Alejandro Colomar
2023-09-25T23:50:23Z

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On Tue, Sep 19, 2023 at 12:02:02PM -0700, Axel Rasmussen wrote:
> Several new features have been added to the kernel recently, and the man
> page wasn't updated to describe these new features. So, add in
> descriptions of any missing features.
>
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
> ---

Patch applied.

Thanks,
Alex

> man2/ioctl_userfaultfd.2 | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
> index e91a1dfc8..53b1f473f 100644
> --- a/man2/ioctl_userfaultfd.2
> +++ b/man2/ioctl_userfaultfd.2
> @@ -204,6 +204,13 @@ If this feature bit is set,
> .I uffd_msg.pagefault.feat.ptid
> will be set to the faulted thread ID for each page-fault message.
> .TP
> +.BR UFFD_FEATURE_PAGEFAULT_FLAG_WP " (since Linux 5.10)"
> +If this feature bit is set,
> +userfaultfd supports write-protect faults
> +for anonymous memory.
> +(Note that shmem / hugetlbfs support
> +is indicated by a separate feature.)
> +.TP
> .BR UFFD_FEATURE_MINOR_HUGETLBFS " (since Linux 5.13)"
> If this feature bit is set,
> the kernel supports registering userfaultfd ranges
> @@ -221,6 +228,22 @@ will be set to the exact page-fault address that was reported by the hardware,
> and will not mask the offset within the page.
> Note that old Linux versions might indicate the exact address as well,
> even though the feature bit is not set.
> +.TP
> +.BR UFFD_FEATURE_WP_HUGETLBFS_SHMEM " (since Linux 5.19)"
> +If this feature bit is set,
> +userfaultfd supports write-protect faults
> +for hugetlbfs and shmem / tmpfs memory.
> +.TP
> +.BR UFFD_FEATURE_WP_UNPOPULATED " (since Linux 6.4)"
> +If this feature bit is set,
> +the kernel will handle anonymous memory the same way as file memory,
> +by allowing the user to write-protect unpopulated ptes.
> +.TP
> +.BR UFFD_FEATURE_POISON " (since Linux 6.6)"
> +If this feature bit is set,
> +the kernel supports resolving faults with the
> +.B UFFDIO_POISON
> +ioctl.
> .PP
> The returned
> .I ioctls
> --
> 2.42.0.459.ge4e396fd5e-goog
>

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