linux-kernel - Re: [RFC PATCH 3/6] mm/vma: Add limits to unmap

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Message-ID: <a32ea375-f093-4f8f-9270-fbe9f7977cc6@lucifer.local>
Date: Tue, 19 Aug 2025 19:48:20 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: David Hildenbrand <david@...hat.com>, maple-tree@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
        Charan Teja Kalla <quic_charante@...cinc.com>,
        shikemeng@...weicloud.com, kasong@...cent.com, nphamcs@...il.com,
        bhe@...hat.com, baohua@...nel.org, chrisl@...nel.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC PATCH 3/6] mm/vma: Add limits to unmap_region() for vmas

On Fri, Aug 15, 2025 at 03:10:28PM -0400, Liam R. Howlett wrote:
> Add a limit to the vma search instead of using the start and end of the
> one passed in.
>
> No functional changes intended.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> ---
>  mm/vma.c | 6 ++++--
>  mm/vma.h | 1 +
>  2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vma.c b/mm/vma.c
> index 3b12c7579831b..fd270345c25d3 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -474,6 +474,7 @@ void remove_vma(struct vm_area_struct *vma)
>   * Called with the mm semaphore held.
>   */
>  void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
> +		unsigned long vma_min, unsigned long vma_max,
>  		struct vm_area_struct *prev, struct vm_area_struct *next)

Luckily we will be getting rid of this as soon as I complete the mmap_prepare +
friends series (_actively_ working on this right now).

Anyway, this is getting quickly horrid, since this is only in vma.c, we could
make this static and pass through map to reduce some of the horror?

We actually can hand it vmi (and thus &vmi->mas via map, so we could implement
it as:

void unmap_region(struct mmap_state *map, struct vm_area_struct *vma,
		  unsigned long min, unsigned long max);

>  {
>  	struct mm_struct *mm = vma->vm_mm;
> @@ -481,7 +482,7 @@ void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
>
>  	tlb_gather_mmu(&tlb, mm);
>  	update_hiwater_rss(mm);
> -	unmap_vmas(&tlb, mas, vma, vma->vm_start, vma->vm_end, vma->vm_end,
> +	unmap_vmas(&tlb, mas, vma, vma_min, vma_max, vma_max,
>  		   /* mm_wr_locked = */ true);
>  	mas_set(mas, vma->vm_end);
>  	free_pgtables(&tlb, mas, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
> @@ -2417,7 +2418,8 @@ static int __mmap_new_file_vma(struct mmap_state *map,
>
>  		vma_iter_set(vmi, vma->vm_end);
>  		/* Undo any partial mapping done by a device driver. */
> -		unmap_region(&vmi->mas, vma, map->prev, map->next);
> +		unmap_region(&vmi->mas, vma, vma->vm_start, vma->vm_end,
> +			     map->prev, map->next);
>
>  		return error;
>  	}
> diff --git a/mm/vma.h b/mm/vma.h
> index b123a9cdedb0d..336dae295853e 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -281,6 +281,7 @@ int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
>  void remove_vma(struct vm_area_struct *vma);
>
>  void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
> +		unsigned long min, unsigned long max,
>  		struct vm_area_struct *prev, struct vm_area_struct *next);
>
>  /* We are about to modify the VMA's flags. */
> --
> 2.47.2
>