linux-kernel - Re: [PATCH] mm/hugetlb: Remove prepare_hugepage

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Message-ID: <jjwzfnbz7uzuniwd2qc6prfg4sboa7dnjswnbeotjbaqngbs6s@2y42bsqcjpv6>
Date: Mon, 30 Jun 2025 10:26:13 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Peter Xu <peterx@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Muchun Song <muchun.song@...ux.dev>,
        Oscar Salvador <osalvador@...e.de>, loongarch@...ts.linux.dev,
        linux-mips@...r.kernel.org, Jason Gunthorpe <jgg@...dia.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH] mm/hugetlb: Remove prepare_hugepage_range()

* Peter Xu <peterx@...hat.com> [250627 12:07]:
> Only mips and loongarch implemented this API, however what it does was
> checking against stack overflow for either len or addr.  That's already
> done in arch's arch_get_unmapped_area*() functions, even though it may not
> be 100% identical checks.
> 
> For example, for both of the architectures, there will be a trivial
> difference on how stack top was defined.  The old code uses STACK_TOP which
> may be slightly smaller than TASK_SIZE on either of them, but the hope is
> that shouldn't be a problem.
> 
> It means the whole API is pretty much obsolete at least now, remove it
> completely.

Thanks for rewording this change, apologies for the late response on
your change log.  I think it's fine.

I think the only meaningful difference is that the failure would have
aborted entirely if stack_top - len < addr, but with this change it will
attempt to search in the opposite direction.  Unless I missed something?

I suspect that this wasn't meant to happen in the first place anyways,
and I bet there are no tests for it and no real-world harm in changing
an error scenario into a potential successful mapping.

Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

> 
> Cc: Liam R. Howlett <Liam.Howlett@...cle.com>
> Cc: Huacai Chen <chenhuacai@...nel.org>
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Muchun Song <muchun.song@...ux.dev>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: loongarch@...ts.linux.dev
> Cc: linux-mips@...r.kernel.org
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> Acked-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  arch/loongarch/include/asm/hugetlb.h | 14 --------------
>  arch/mips/include/asm/hugetlb.h      | 14 --------------
>  fs/hugetlbfs/inode.c                 |  8 ++------
>  include/asm-generic/hugetlb.h        |  8 --------
>  include/linux/hugetlb.h              |  6 ------
>  5 files changed, 2 insertions(+), 48 deletions(-)
> 
> diff --git a/arch/loongarch/include/asm/hugetlb.h b/arch/loongarch/include/asm/hugetlb.h
> index 4dc4b3e04225..ab68b594f889 100644
> --- a/arch/loongarch/include/asm/hugetlb.h
> +++ b/arch/loongarch/include/asm/hugetlb.h
> @@ -10,20 +10,6 @@
>  
>  uint64_t pmd_to_entrylo(unsigned long pmd_val);
>  
> -#define __HAVE_ARCH_PREPARE_HUGEPAGE_RANGE
> -static inline int prepare_hugepage_range(struct file *file,
> -					 unsigned long addr,
> -					 unsigned long len)
> -{
> -	unsigned long task_size = STACK_TOP;
> -
> -	if (len > task_size)
> -		return -ENOMEM;
> -	if (task_size - len < addr)
> -		return -EINVAL;
> -	return 0;
> -}
> -
>  #define __HAVE_ARCH_HUGE_PTE_CLEAR
>  static inline void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
>  				  pte_t *ptep, unsigned long sz)
> diff --git a/arch/mips/include/asm/hugetlb.h b/arch/mips/include/asm/hugetlb.h
> index fbc71ddcf0f6..8c460ce01ffe 100644
> --- a/arch/mips/include/asm/hugetlb.h
> +++ b/arch/mips/include/asm/hugetlb.h
> @@ -11,20 +11,6 @@
>  
>  #include <asm/page.h>
>  
> -#define __HAVE_ARCH_PREPARE_HUGEPAGE_RANGE
> -static inline int prepare_hugepage_range(struct file *file,
> -					 unsigned long addr,
> -					 unsigned long len)
> -{
> -	unsigned long task_size = STACK_TOP;
> -
> -	if (len > task_size)
> -		return -ENOMEM;
> -	if (task_size - len < addr)
> -		return -EINVAL;
> -	return 0;
> -}
> -
>  #define __HAVE_ARCH_HUGE_PTEP_GET_AND_CLEAR
>  static inline pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
>  					    unsigned long addr, pte_t *ptep,
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 00b2d1a032fd..81a6acddd690 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -179,12 +179,8 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>  
>  	if (len & ~huge_page_mask(h))
>  		return -EINVAL;
> -	if (flags & MAP_FIXED) {
> -		if (addr & ~huge_page_mask(h))
> -			return -EINVAL;
> -		if (prepare_hugepage_range(file, addr, len))
> -			return -EINVAL;
> -	}
> +	if ((flags & MAP_FIXED) && (addr & ~huge_page_mask(h)))
> +		return -EINVAL;
>  	if (addr)
>  		addr0 = ALIGN(addr, huge_page_size(h));
>  
> diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
> index 3e0a8fe9b108..4bce4f07f44f 100644
> --- a/include/asm-generic/hugetlb.h
> +++ b/include/asm-generic/hugetlb.h
> @@ -114,14 +114,6 @@ static inline int huge_pte_none_mostly(pte_t pte)
>  }
>  #endif
>  
> -#ifndef __HAVE_ARCH_PREPARE_HUGEPAGE_RANGE
> -static inline int prepare_hugepage_range(struct file *file,
> -		unsigned long addr, unsigned long len)
> -{
> -	return 0;
> -}
> -#endif
> -
>  #ifndef __HAVE_ARCH_HUGE_PTEP_SET_WRPROTECT
>  static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
>  		unsigned long addr, pte_t *ptep)
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index c6c87eae4a8d..474de8e2a8f2 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -359,12 +359,6 @@ static inline void hugetlb_show_meminfo_node(int nid)
>  {
>  }
>  
> -static inline int prepare_hugepage_range(struct file *file,
> -				unsigned long addr, unsigned long len)
> -{
> -	return -EINVAL;
> -}
> -
>  static inline void hugetlb_vma_lock_read(struct vm_area_struct *vma)
>  {
>  }
> -- 
> 2.49.0
> 
>