linux-kernel - Re: [PATCH V13 2/6] mm: userfaultfd: Add pgtable_supports_uffd

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Message-ID: <bc87f2a8-7a9c-4416-9106-bdf4b98e40a8@redhat.com>
Date: Wed, 17 Sep 2025 09:25:09 +0200
From: David Hildenbrand <david@...hat.com>
To: Chunyan Zhang <zhangchunyan@...as.ac.cn>,
 linux-riscv@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>, Conor Dooley <conor@...nel.org>,
 Deepak Gupta <debug@...osinc.com>, Ved Shanbhogue <ved@...osinc.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Andrew Morton <akpm@...ux-foundation.org>, Peter Xu <peterx@...hat.com>,
 Arnd Bergmann <arnd@...db.de>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Axel Rasmussen <axelrasmussen@...gle.com>, Yuanchu Xie <yuanchu@...gle.com>,
 Chunyan Zhang <zhang.lyra@...il.com>
Subject: Re: [PATCH V13 2/6] mm: userfaultfd: Add pgtable_supports_uffd_wp()

On 17.09.25 05:36, Chunyan Zhang wrote:
> Some platforms can customize the PTE/PMD entry uffd-wp bit making
> it unavailable even if the architecture provides the resource.
> This patch adds a macro API that allows architectures to define their
> specific implementations to check if the uffd-wp bit is available
> on which device the kernel is running.
> 
> Also this patch is removing "ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP" and
> "ifdef CONFIG_PTE_MARKER_UFFD_WP" in favor of pgtable_supports_uffd_wp()
> and uffd_supports_wp_marker() checks respectively that default to
> IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) and
> "IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) && IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP)"
> if not overridden by the architecture, no change in behavior is expected.
> 
> Acked-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Chunyan Zhang <zhangchunyan@...as.ac.cn>
> ---

[...]

Taking another look.

>   /* mm helpers */
> @@ -415,68 +475,24 @@ static inline bool vma_has_uffd_without_event_remap(struct vm_area_struct *vma)
>   	return false;
>   }
>   
> -#endif /* CONFIG_USERFAULTFD */
> -
>   static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma)
>   {
> -	/* Only wr-protect mode uses pte markers */
> -	if (!userfaultfd_wp(vma))
>   		return false;

Isn't this indented one level too deep?

> -
> -	/* File-based uffd-wp always need markers */
> -	if (!vma_is_anonymous(vma))
> -		return true;
> -
> -	/*
> -	 * Anonymous uffd-wp only needs the markers if WP_UNPOPULATED
> -	 * enabled (to apply markers on zero pages).
> -	 */
> -	return userfaultfd_wp_unpopulated(vma);
>   }
>   
>   static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry)
>   {
> -#ifdef CONFIG_PTE_MARKER_UFFD_WP
> -	return is_pte_marker_entry(entry) &&
> -	    (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
> -#else
> -	return false;
> -#endif
> +		return false;

Same here.

>   }
>   
>   static inline bool pte_marker_uffd_wp(pte_t pte)
>   {
> -#ifdef CONFIG_PTE_MARKER_UFFD_WP
> -	swp_entry_t entry;
> -
> -	if (!is_swap_pte(pte))
>   		return false;

Same here.

> -
> -	entry = pte_to_swp_entry(pte);
> -
> -	return pte_marker_entry_uffd_wp(entry);
> -#else
> -	return false;
> -#endif
>   }

-- 
Cheers

David / dhildenb