linux-kernel - Re: [PATCH v6 04/23] mm/uffd: PTE_MARKER_UFFD

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Message-ID: <1966495.R0KUr5dvoW@nvdebian>
Date:   Thu, 16 Dec 2021 16:18:50 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Peter Xu <peterx@...hat.com>
CC:     Axel Rasmussen <axelrasmussen@...gle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Hugh Dickins <hughd@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Jerome Glisse <jglisse@...hat.com>,
        "Matthew Wilcox" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>, <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH v6 04/23] mm/uffd: PTE_MARKER_UFFD_WP

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
>