Re: [PATCH 22/30] mm/vma: move __install_special_mapping() to vma.c

On Thu, Jul 02, 2026 at 12:22:56PM +0100, Pedro Falcato wrote:
> On Mon, Jun 29, 2026 at 01:23:33PM +0100, Lorenzo Stoakes wrote:
> > This function is operating on VMAs and rightly belongs in vma.c, where it
> > can be subject to VMA userland testing and allows us to isolate it from the
> > rest of mm.
> >
> > The _install_special_mapping() function will remain in mmap.c as a wrapper,
> > since this is used by architecture-specific code.
> >
> > Doing so allows us to isolate more functions in vma.c for the same reasons.
> >
> > This forms part of work to allow for tracking MAP_PRIVATE file-backed
> > mappings by their anonymous virtual page offset, as doing so allows us to
> > isolate and keep code that interacts with this together.
> >
> > No functional change intended.
> >
> > Signed-off-by: Lorenzo Stoakes <[email protected]>
> > ---
> >  mm/mmap.c | 38 --------------------------------------
> >  mm/vma.c  | 38 ++++++++++++++++++++++++++++++++++++++
> >  mm/vma.h  |  5 +++++
> >  3 files changed, 43 insertions(+), 38 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 2d09a57e3620..46174e706bbe 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -1447,44 +1447,6 @@ static vm_fault_t special_mapping_fault(struct vm_fault *vmf)
> >  	return VM_FAULT_SIGBUS;
> >  }
> >
> > -static struct vm_area_struct *__install_special_mapping(
> > -	struct mm_struct *mm,
> > -	unsigned long addr, unsigned long len,
> > -	vm_flags_t vm_flags, void *priv,
> > -	const struct vm_operations_struct *ops)
> > -{
> > -	int ret;
> > -	struct vm_area_struct *vma;
> > -
> > -	vma = vm_area_alloc(mm);
> > -	if (unlikely(vma == NULL))
> > -		return ERR_PTR(-ENOMEM);
> > -
> > -	vma_set_range(vma, addr, addr + len, 0);
> > -	vm_flags |= mm->def_flags | VM_DONTEXPAND;
> > -	if (pgtable_supports_soft_dirty())
> > -		vm_flags |= VM_SOFTDIRTY;
> > -	vm_flags_init(vma, vm_flags & ~VM_LOCKED_MASK);
> > -	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> > -
> > -	vma->vm_ops = ops;
> > -	vma->vm_private_data = priv;
> > -
> > -	ret = insert_vm_struct(mm, vma);
> > -	if (ret)
> > -		goto out;
> > -
> > -	vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);
> > -
> > -	perf_event_mmap(vma);
> > -
> > -	return vma;
> > -
> > -out:
> > -	vm_area_free(vma);
> > -	return ERR_PTR(ret);
> > -}
> > -
> >  bool vma_is_special_mapping(const struct vm_area_struct *vma,
> >  	const struct vm_special_mapping *sm)
> >  {
> > diff --git a/mm/vma.c b/mm/vma.c
> > index cb7222e20c93..f4de706a2728 100644
> > --- a/mm/vma.c
> > +++ b/mm/vma.c
> > @@ -3399,3 +3399,41 @@ __weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
> >  {
> >  	return vma_kernel_pagesize(vma);
> >  }
> > +
> > +struct vm_area_struct *__install_special_mapping(
> > +	struct mm_struct *mm,
> > +	unsigned long addr, unsigned long len,
> > +	vm_flags_t vm_flags, void *priv,
> > +	const struct vm_operations_struct *ops)
> > +{
> > +	int ret;
> > +	struct vm_area_struct *vma;
> > +
> > +	vma = vm_area_alloc(mm);
> > +	if (unlikely(vma == NULL))
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	vma_set_range(vma, addr, addr + len, 0);
> > +	vm_flags |= mm->def_flags | VM_DONTEXPAND;
> > +	if (pgtable_supports_soft_dirty())
> > +		vm_flags |= VM_SOFTDIRTY;
> > +	vm_flags_init(vma, vm_flags & ~VM_LOCKED_MASK);
> > +	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> > +
> > +	vma->vm_ops = ops;
> > +	vma->vm_private_data = priv;
> > +
> > +	ret = insert_vm_struct(mm, vma);
> > +	if (ret)
> > +		goto out;
> > +
> > +	vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);
> > +
> > +	perf_event_mmap(vma);
> > +
> > +	return vma;
> > +
> > +out:
> > +	vm_area_free(vma);
> > +	return ERR_PTR(ret);
> > +}
> > diff --git a/mm/vma.h b/mm/vma.h
> > index 47fe35e5307e..14f026bf3be4 100644
> > --- a/mm/vma.h
> > +++ b/mm/vma.h
> > @@ -775,4 +775,9 @@ static inline bool map_deny_write_exec(const vma_flags_t *old,
> >  }
> >  #endif
> >
> > +struct vm_area_struct *__install_special_mapping(struct mm_struct *mm,
> > +		unsigned long addr, unsigned long len,
> > +		vm_flags_t vm_flags, void *priv,
> > +		const struct vm_operations_struct *ops);
> > +
> >  #endif	/* __MM_VMA_H */
>
> I'm really annoyed that _install_special_mapping has a leading underscore.
> That's it.

Yeah it's horrible :)

>
> Reviewed-by: Pedro Falcato <[email protected]>

Thanks!

>
> --
> Pedro

Cheers, Lorenzo