linux-kernel - Re: [PATCH v2 3/4] mm/hugetlb: Support vm_uffd

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Message-ID: <aGD-wUFX9oSIFm3e@kernel.org>
Date: Sun, 29 Jun 2025 11:52:17 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Peter Xu <peterx@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Houghton <jthoughton@...gle.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Nikita Kalyazin <kalyazin@...zon.com>,
	Michal Hocko <mhocko@...e.com>,
	David Hildenbrand <david@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Oscar Salvador <osalvador@...e.de>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	Ujwal Kundur <ujwal.kundur@...il.com>
Subject: Re: [PATCH v2 3/4] mm/hugetlb: Support vm_uffd_ops API

On Fri, Jun 27, 2025 at 11:46:54AM -0400, Peter Xu wrote:
> Add support for the new vm_uffd_ops API for hugetlb.  Note that this only
> introduces the support, the API is not yet used by core mm.
> 
> Due to legacy reasons, it's still not trivial to move hugetlb completely to
> the API (like shmem).  But it will still use uffd_features and uffd_ioctls
> properly on the API because that's pretty general.
> 
> Cc: Muchun Song <muchun.song@...ux.dev>
> Cc: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: Peter Xu <peterx@...hat.com>

Acked-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
>  mm/hugetlb.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 11d5668ff6e7..ccd2be152d36 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5457,6 +5457,22 @@ static vm_fault_t hugetlb_vm_op_fault(struct vm_fault *vmf)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_USERFAULTFD
> +static const vm_uffd_ops hugetlb_uffd_ops = {
> +	.uffd_features	= 	__VM_UFFD_FLAGS,
> +	/* _UFFDIO_ZEROPAGE not supported */
> +	.uffd_ioctls	= 	BIT(_UFFDIO_COPY) |
> +				BIT(_UFFDIO_WRITEPROTECT) |
> +				BIT(_UFFDIO_CONTINUE) |
> +				BIT(_UFFDIO_POISON),
> +	/*
> +	 * Hugetlbfs still has its own hard-coded handler in userfaultfd,
> +	 * due to limitations similar to vm_operations_struct.fault().
> +	 * TODO: generalize it to use the API functions.
> +	 */
> +};
> +#endif
> +
>  /*
>   * When a new function is introduced to vm_operations_struct and added
>   * to hugetlb_vm_ops, please consider adding the function to shm_vm_ops.
> @@ -5470,6 +5486,9 @@ const struct vm_operations_struct hugetlb_vm_ops = {
>  	.close = hugetlb_vm_op_close,
>  	.may_split = hugetlb_vm_op_split,
>  	.pagesize = hugetlb_vm_op_pagesize,
> +#ifdef CONFIG_USERFAULTFD
> +	.userfaultfd_ops = &hugetlb_uffd_ops,
> +#endif
>  };
>  
>  static pte_t make_huge_pte(struct vm_area_struct *vma, struct folio *folio,
> -- 
> 2.49.0
> 

-- 
Sincerely yours,
Mike.