linux-kernel - Re: [PATCH V12 2/5] mm: userfaultfd: Add pgtable_supports_uffd

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Message-ID: <37c8dd09-e0b1-4f76-a03b-4548c1fe4796@redhat.com>
Date: Mon, 15 Sep 2025 15:56:13 +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>, 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 V12 2/5] mm: userfaultfd: Add pgtable_supports_uffd_wp()

On 15.09.25 12:13, 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.
> 

Similar to my reply to #1, you should probably summarize what you do 
regarding ifdef and "No functional change expected".

> Signed-off-by: Chunyan Zhang <zhangchunyan@...as.ac.cn>
> ---

[...]

LGTM, one not below, thanks!

Acked-by: David Hildenbrand <david@...hat.com>

> +/*
> + * Some platforms can customize the uffd-wp bit, making it unavailable
> + * even if the architecture provides the resource.
> + * Adding this API allows architectures to add their own checks for the
> + * devices on which the kernel is running.
> + * Note: When overriding it, please make sure the
> + * CONFIG_HAVE_ARCH_USERFAULTFD_WP is part of this macro.
> + */
> +#ifndef pgtable_supports_uffd_wp
> +#define pgtable_supports_uffd_wp()	IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP)
> +#endif
> +
> +static __always_inline bool uffd_supports_wp_marker(void)
> +{
> +	return pgtable_supports_uffd_wp() && IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP);
> +}

Likely a simple "inline" should do the trick?

> +
>   #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
>   static __always_inline int pte_uffd_wp(pte_t pte)
>   {
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> index 89b518ff097e..d6526a7f034b 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -570,9 +570,15 @@ static inline bool
>   pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
>   			      pte_t *pte, pte_t pteval)
>   {

-- 
Cheers

David / dhildenb