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

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Message-ID: <dc483db3-be4d-45f7-8b40-a28f5d8f5738@suse.cz>
Date: Thu, 27 Nov 2025 18:29:39 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>,
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Subject: Re: [PATCH v3 14/16] mm: remove is_hugetlb_entry_[migration,
 hwpoisoned]()

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.

>  
> -	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 */
>