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

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Message-ID: <CAAfSe-vjgcgFyvVoci8F9ra4JwbDcdbhsxjSL0j8=0CCKAzFHQ@mail.gmail.com>
Date: Wed, 17 Sep 2025 17:20:14 +0800
From: Chunyan Zhang <zhang.lyra@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: 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, 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>
Subject: Re: [PATCH V13 2/6] mm: userfaultfd: Add pgtable_supports_uffd_wp()

On Wed, 17 Sept 2025 at 15:25, David Hildenbrand <david@...hat.com> wrote:
>
> 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?

Oh right, I will fix these.

Thanks to you spotting them out!

Chunyan

>
> > -
> > -     /* 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
>