linux-kernel - Re: [PATCH v3 14/16] mm: remove is_hugetlb_entry

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Message-ID: <aae888f2-e826-42ad-a35f-dbcb15fd4126@lucifer.local>
Date: Thu, 27 Nov 2025 17:41:12 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH v3 14/16] mm: remove is_hugetlb_entry_[migration,
 hwpoisoned]()

On Thu, Nov 27, 2025 at 06:29:39PM +0100, Vlastimil Babka wrote:
> On 11/10/25 23:21, Lorenzo Stoakes wrote:
> > We do not need to have explicit helper functions for these, it adds a level
> > of confusion and indirection when we can simply use software leaf entry
> > logic here instead and spell out the special huge_pte_none() case we must
> > consider.
> >
> > No functional change intended.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
>
> But seems to me a fixup is needed:
>
> > ---
> >  fs/proc/task_mmu.c      | 19 +++++----
> >  include/linux/hugetlb.h |  2 -
> >  mm/hugetlb.c            | 91 +++++++++++++++++------------------------
> >  mm/mempolicy.c          | 17 +++++---
> >  mm/migrate.c            | 15 +++++--
> >  5 files changed, 69 insertions(+), 75 deletions(-)
> >
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 6cb9e1691e18..3cdefa7546db 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -2499,22 +2499,23 @@ static void make_uffd_wp_huge_pte(struct vm_area_struct *vma,
> >  				  unsigned long addr, pte_t *ptep,
> >  				  pte_t ptent)
> >  {
> > -	unsigned long psize;
> > +	const unsigned long psize = huge_page_size(hstate_vma(vma));
> > +	softleaf_t entry;
> >
> > -	if (is_hugetlb_entry_hwpoisoned(ptent) || pte_is_marker(ptent))
> > -		return;
> > +	if (huge_pte_none(ptent))
> > +		set_huge_pte_at(vma->vm_mm, addr, ptep,
> > +				make_pte_marker(PTE_MARKER_UFFD_WP), psize);
>
> Shouldn't we return here? Otherwise AFAICS we'll also reach the
> huge_ptep_modify_prot_commit() below and that wasn't happening before.

Yup, will reply with fix-patch, thanks.

>
> >
> > -	psize = huge_page_size(hstate_vma(vma));
> > +	entry = softleaf_from_pte(ptent);
> > +	if (softleaf_is_hwpoison(entry) || softleaf_is_marker(entry))
> > +		return;
> >
> > -	if (is_hugetlb_entry_migration(ptent))
> > +	if (softleaf_is_migration(entry))
> >  		set_huge_pte_at(vma->vm_mm, addr, ptep,
> >  				pte_swp_mkuffd_wp(ptent), psize);
> > -	else if (!huge_pte_none(ptent))
> > +	else
> >  		huge_ptep_modify_prot_commit(vma, addr, ptep, ptent,
> >  					     huge_pte_mkuffd_wp(ptent));
> > -	else
> > -		set_huge_pte_at(vma->vm_mm, addr, ptep,
> > -				make_pte_marker(PTE_MARKER_UFFD_WP), psize);
> >  }
> >  #endif /* CONFIG_HUGETLB_PAGE */
> >