linux-kernel - Re: [PATCH 06/10] ioctl_userfaultfd.2: describe missing UFFDIO

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Message-ID: <20231009084514.GJ3303@kernel.org>
Date:   Mon, 9 Oct 2023 11:45:14 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alejandro Colomar <alx@...nel.org>, Peter Xu <peterx@...hat.com>,
        linux-man@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/10] ioctl_userfaultfd.2: describe missing UFFDIO_API
 feature flags

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@...gle.com>

Reviewed-by: Mike Rapoport (IBM) <rppt@...nel.org>

with a small nit below

> ---
>  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.

Nit: s/ptes/page table entries/

> +.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
> 
> 

-- 
Sincerely yours,
Mike.