Re: [PATCH v6 04/23] mm/uffd: PTE_MARKER_UFFD_WP

Alistair Popple
2021-12-16T05:19:02Z

On Monday, 15 November 2021 6:55:03 PM AEDT Peter Xu wrote:

[...]

> +/*
> + * Returns true if this is a swap pte and was uffd-wp wr-protected in either
> + * forms (pte marker or a normal swap pte), false otherwise.
> + */
> +static inline bool pte_swp_uffd_wp_any(pte_t pte)
> +{
> +#ifdef CONFIG_PTE_MARKER_UFFD_WP
> + if (!is_swap_pte(pte))
> + return false;
> +
> + if (pte_swp_uffd_wp(pte))
> + return true;

If I'm not mistaken normal swap uffd-wp ptes can still exist when
CONFIG_PTE_MARKER_UFFD_WP=n so shouldn't this be outside the #ifdef protection?

In fact we could drop the #ifdef entirely here as it is safe to call
is_pte_marker_uffd_wp() without CONFIG_PTE_MARKER_UFFD_WP.

> +
> + if (is_pte_marker_uffd_wp(pte))
> + return true;
> +#endif
> + return false;
> +}
> +
> #endif /* _LINUX_USERFAULTFD_K_H */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 66f23c6c2032..f01c8e0afadf 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -904,6 +904,15 @@ config PTE_MARKER
> help
> Allows to create marker PTEs for file-backed memory.
>
> +config PTE_MARKER_UFFD_WP
> + bool "Marker PTEs support for userfaultfd write protection"
> + depends on PTE_MARKER && HAVE_ARCH_USERFAULTFD_WP
> +
> + help
> + Allows to create marker PTEs for userfaultfd write protection
> + purposes. It is required to enable userfaultfd write protection on
> + file-backed memory types like shmem and hugetlbfs.
> +
> source "mm/damon/Kconfig"
>
> endmenu
>