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

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Message-ID: <w43jgvlabgvxpq2jb3zv7zo64r4xbvmad7cf75l3keests7djf@lmqslvejyyk4>
Date: Wed, 3 Sep 2025 15:57:37 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...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

* Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [250819 14:48]:
> 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);
> 

Ah... I could do this on top of the last patch.. that might be more
clear?

> >  {
> >  	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
> >