Re: [PATCH 17/30] mm: prefer vma_[start,end]_pgoff() to vma->vm_pgoff in kernel/

[Lorenzo Stoakes <ljs@kernel.org>]

On Thu, Jul 02, 2026 at 12:01:37PM +0100, Pedro Falcato wrote:
> On Mon, Jun 29, 2026 at 01:23:28PM +0100, Lorenzo Stoakes wrote:
> > Be consistent in using vma_start_pgoff() and vma_end_pgoff(), which clearly
> > indicates which part of the VMA the page offset refers to and aids
> > greppability.
> >
> > This is part of a broader series laying the ground to provide a virtual
> > page offset for MAP_PRIVATE-file backed anon folios.
> >
> > No functional change intended.
> >
> > Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
> > ---
> >  kernel/dma/coherent.c      |  7 ++++---
> >  kernel/dma/direct.c        |  6 ++++--
> >  kernel/dma/mapping.c       |  8 +++++---
> >  kernel/dma/ops_helpers.c   |  4 ++--
> >  kernel/events/core.c       | 20 +++++++++++---------
> >  kernel/events/uprobes.c    | 11 +++++++----
> >  kernel/kcov.c              |  2 +-
> >  kernel/trace/ring_buffer.c |  3 ++-
> >  8 files changed, 36 insertions(+), 25 deletions(-)
> >
> > diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c
> > index bcdc0f76d2e8..2d3195eb7e83 100644
> > --- a/kernel/dma/coherent.c
> > +++ b/kernel/dma/coherent.c
> > @@ -236,14 +236,15 @@ static int __dma_mmap_from_coherent(struct dma_coherent_mem *mem,
> >  {
> >  	if (mem && vaddr >= mem->virt_base && vaddr + size <=
> >  		   (mem->virt_base + ((dma_addr_t)mem->size << PAGE_SHIFT))) {
> > -		unsigned long off = vma->vm_pgoff;
> > +		const pgoff_t pgoff_start = vma_start_pgoff(vma);
> > +		const pgoff_t pgoff_end = vma_end_pgoff(vma);
> >  		int start = (vaddr - mem->virt_base) >> PAGE_SHIFT;
> >  		unsigned long user_count = vma_pages(vma);
> >  		int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> >
> >  		*ret = -ENXIO;
> > -		if (off < count && user_count <= count - off) {
> > -			unsigned long pfn = mem->pfn_base + start + off;
> > +		if (pgoff_start < count && pgoff_end <= count) {
> > +			unsigned long pfn = mem->pfn_base + start + pgoff_start;
> >  			*ret = remap_pfn_range(vma, vma->vm_start, pfn,
> >  					       user_count << PAGE_SHIFT,
> >  					       vma->vm_page_prot);
> > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> > index 4391b797d4db..436310d6e4a2 100644
> > --- a/kernel/dma/direct.c
> > +++ b/kernel/dma/direct.c
> > @@ -534,6 +534,8 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
> >  	unsigned long user_count = vma_pages(vma);
> >  	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> >  	unsigned long pfn = PHYS_PFN(dma_to_phys(dev, dma_addr));
> > +	const pgoff_t pgoff_start = vma_start_pgoff(vma);
> > +	const pgoff_t pgoff_end = vma_end_pgoff(vma);
> >  	int ret = -ENXIO;
> >
> >  	vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, attrs);
> > @@ -545,9 +547,9 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
> >  	if (dma_mmap_from_global_coherent(vma, cpu_addr, size, &ret))
> >  		return ret;
> >
> > -	if (vma->vm_pgoff >= count || user_count > count - vma->vm_pgoff)
> > +	if (pgoff_start >= count || pgoff_end > count)
> >  		return -ENXIO;
> > -	return remap_pfn_range(vma, vma->vm_start, pfn + vma->vm_pgoff,
> > +	return remap_pfn_range(vma, vma->vm_start, pfn + pgoff_start,
> >  			user_count << PAGE_SHIFT, vma->vm_page_prot);
> >  }
> >
> > diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> > index 4fe04669e5e6..c986639044e9 100644
> > --- a/kernel/dma/mapping.c
> > +++ b/kernel/dma/mapping.c
> > @@ -761,12 +761,14 @@ EXPORT_SYMBOL_GPL(dma_free_pages);
> >  int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma,
> >  		size_t size, struct page *page)
> >  {
> > -	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> > +	const pgoff_t pgoff_start = vma_start_pgoff(vma);
> > +	const pgoff_t pgoff_end = vma_end_pgoff(vma);
> > +	const unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> >
> > -	if (vma->vm_pgoff >= count || vma_pages(vma) > count - vma->vm_pgoff)
> > +	if (pgoff_start >= count || pgoff_end > count)
> >  		return -ENXIO;
> >  	return remap_pfn_range(vma, vma->vm_start,
> > -			       page_to_pfn(page) + vma->vm_pgoff,
> > +			       page_to_pfn(page) + pgoff_start,
> >  			       vma_pages(vma) << PAGE_SHIFT, vma->vm_page_prot);
> >  }
> >  EXPORT_SYMBOL_GPL(dma_mmap_pages);
> > diff --git a/kernel/dma/ops_helpers.c b/kernel/dma/ops_helpers.c
> > index 20caf9cabf69..6b5f9208d31c 100644
> > --- a/kernel/dma/ops_helpers.c
> > +++ b/kernel/dma/ops_helpers.c
> > @@ -39,7 +39,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
> >  #ifdef CONFIG_MMU
> >  	unsigned long user_count = vma_pages(vma);
> >  	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> > -	unsigned long off = vma->vm_pgoff;
> > +	unsigned long off = vma_start_pgoff(vma);
> >  	struct page *page = dma_common_vaddr_to_page(cpu_addr);
> >  	int ret = -ENXIO;
> >
> > @@ -52,7 +52,7 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
> >  		return -ENXIO;
> >
> >  	return remap_pfn_range(vma, vma->vm_start,
> > -			page_to_pfn(page) + vma->vm_pgoff,
> > +			page_to_pfn(page) + vma_start_pgoff(vma),
> >  			user_count << PAGE_SHIFT, vma->vm_page_prot);
> >  #else
> >  	return -ENXIO;
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 954c36e28101..d6d2d557ccb8 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -6998,7 +6998,7 @@ static void perf_mmap_open(struct vm_area_struct *vma)
> >  	refcount_inc(&event->mmap_count);
> >  	refcount_inc(&event->rb->mmap_count);
> >
> > -	if (vma->vm_pgoff)
> > +	if (vma_start_pgoff(vma))
> >  		refcount_inc(&event->rb->aux_mmap_count);
> >
> >  	if (mapped)
> > @@ -7032,7 +7032,7 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> >  	 * The AUX buffer is strictly a sub-buffer, serialize using aux_mutex
> >  	 * to avoid complications.
> >  	 */
> > -	if (rb_has_aux(rb) && vma->vm_pgoff == rb->aux_pgoff &&
> > +	if (rb_has_aux(rb) && vma_start_pgoff(vma) == rb->aux_pgoff &&
> >  	    refcount_dec_and_mutex_lock(&rb->aux_mmap_count, &rb->aux_mutex)) {
> >  		/*
> >  		 * Stop all AUX events that are writing to this buffer,
> > @@ -7190,7 +7190,8 @@ static int map_range(struct perf_buffer *rb, struct vm_area_struct *vma)
> >  	 */
> >  	for (pagenum = 0; pagenum < nr_pages; pagenum++) {
> >  		unsigned long va = vma->vm_start + PAGE_SIZE * pagenum;
> > -		struct page *page = perf_mmap_to_page(rb, vma->vm_pgoff + pagenum);
> > +		struct page *page = perf_mmap_to_page(rb,
> > +				vma_start_pgoff(vma) + pagenum);
> >
> >  		if (page == NULL) {
> >  			err = -EINVAL;
> > @@ -7348,6 +7349,7 @@ static int perf_mmap_aux(struct vm_area_struct *vma, struct perf_event *event,
> >  	u64 aux_offset, aux_size;
> >  	struct perf_buffer *rb;
> >  	int ret, rb_flags = 0;
> > +	const pgoff_t pgoff_start = vma_start_pgoff(vma);
>
> Variable decs here seem to be in reverse christmas tree order, so perhaps
> move this to the top.

Ack will change on respin.

>
> >
> >  	rb = event->rb;
> >  	if (!rb)
> > @@ -7366,11 +7368,11 @@ static int perf_mmap_aux(struct vm_area_struct *vma, struct perf_event *event,
> >  	if (aux_offset < perf_data_size(rb) + PAGE_SIZE)
> >  		return -EINVAL;
> >
> > -	if (aux_offset != vma->vm_pgoff << PAGE_SHIFT)
> > +	if (aux_offset != pgoff_start << PAGE_SHIFT)
> >  		return -EINVAL;
> >
> >  	/* already mapped with a different offset */
> > -	if (rb_has_aux(rb) && rb->aux_pgoff != vma->vm_pgoff)
> > +	if (rb_has_aux(rb) && rb->aux_pgoff != pgoff_start)
> >  		return -EINVAL;
> >
> >  	if (aux_size != nr_pages * PAGE_SIZE)
> > @@ -7400,7 +7402,7 @@ static int perf_mmap_aux(struct vm_area_struct *vma, struct perf_event *event,
> >  		if (vma->vm_flags & VM_WRITE)
> >  			rb_flags |= RING_BUFFER_WRITABLE;
> >
> > -		ret = rb_alloc_aux(rb, event, vma->vm_pgoff, nr_pages,
> > +		ret = rb_alloc_aux(rb, event, pgoff_start, nr_pages,
> >  				   event->attr.aux_watermark, rb_flags);
> >  		if (ret) {
> >  			refcount_dec(&rb->mmap_count);
> > @@ -7457,7 +7459,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
> >  		if (event->state <= PERF_EVENT_STATE_REVOKED)
> >  			return -ENODEV;
> >
> > -		if (vma->vm_pgoff == 0)
> > +		if (!vma_start_pgoff(vma))
> >  			ret = perf_mmap_rb(vma, event, nr_pages);
> >  		else
> >  			ret = perf_mmap_aux(vma, event, nr_pages);
> > @@ -9884,7 +9886,7 @@ static bool perf_addr_filter_vma_adjust(struct perf_addr_filter *filter,
> >  					struct perf_addr_filter_range *fr)
> >  {
> >  	unsigned long vma_size = vma->vm_end - vma->vm_start;
> > -	unsigned long off = vma->vm_pgoff << PAGE_SHIFT;
> > +	unsigned long off = vma_start_pgoff(vma) << PAGE_SHIFT;
> >  	struct file *file = vma->vm_file;
> >
> >  	if (!perf_addr_filter_match(filter, file, off, vma_size))
> > @@ -9974,7 +9976,7 @@ void perf_event_mmap(struct vm_area_struct *vma)
> >  			/* .tid */
> >  			.start  = vma->vm_start,
> >  			.len    = vma->vm_end - vma->vm_start,
> > -			.pgoff  = (u64)vma->vm_pgoff << PAGE_SHIFT,
> > +			.pgoff  = (u64)vma_start_pgoff(vma) << PAGE_SHIFT,
> >  		},
> >  		/* .maj (attr_mmap2 only) */
> >  		/* .min (attr_mmap2 only) */
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index f23cebacbc6d..244651380ca1 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -144,12 +144,14 @@ static bool valid_vma(struct vm_area_struct *vma, bool is_register)
> >
> >  static unsigned long offset_to_vaddr(struct vm_area_struct *vma, loff_t offset)
> >  {
> > -	return vma->vm_start + offset - ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
> > +	return vma->vm_start + offset -
> > +		((loff_t)vma_start_pgoff(vma) << PAGE_SHIFT);
> >  }
> >
> >  static loff_t vaddr_to_offset(struct vm_area_struct *vma, unsigned long vaddr)
> >  {
> > -	return ((loff_t)vma->vm_pgoff << PAGE_SHIFT) + (vaddr - vma->vm_start);
> > +	return ((loff_t)vma_start_pgoff(vma) << PAGE_SHIFT) +
> > +		(vaddr - vma->vm_start);
> >  }
>
> Something we've seen in this series is that perhaps something like
>
> static inline loff_t vma_start_off(vma)
> {
> 	return ((loff_t) vma_start_pgoff(vma)) << PAGE_SHIFT;
> }
>
> could be worth it.

Yeah I already thought about this kind of thing, but in the end decided against
it at least for now, maybe I could revisit with something like that added
though...

But given this series is being held off on already for acceptance, I'm not sure
adding _yet more_ changes will be welcomed.

Plus I worry people will get confused.

There's 2 forms I noticed:

1. effectively: linear_page_index(vma, address) << PAGE_SHIFT

I wanted to rewrite this as such, but you can't, because of course vaddr might
have non-page aligned bits (or tags) that you lose by doing that. So ugh.

You'd then need to write a slightly nuanced version like:

static inline unsigned long vma_offset(const struct vm_area_struct *vma,
				       const unsigned long address)
{
	/* Retains page offset and tags. */
	return address - vma->vm_start;
}

static inline unsigned long linear_page_offset(const struct vm_area_struct *vma,
					       const unsigned long address)
{
	const unsigned long addr = vma_start_pgoff(vma) << PAGE_SHIFT;

	addr += linear_delta(vma, address);
	return addr;
}

(Could also do:)

static inline pgoff_t linear_page_delta(const struct vm_area_struct *vma,
					const unsigned long address)
{
	return vma_offset(vma, address) >> PAGE_SHIFT;
}

BUT.

I think this will confuse people. I already in a previous version of this series
named linear_page_delta() as linear_page_offset() and then changed it to avoid
confusion.

And I'm not sure it's really all that useful. Perhaps retaining vma_offset()
would be though.

2.

This is a much more useful form I noticed, effectively drivers doing the inverse
of a linear_page_index() to get the address:

static inline unsigned long linear_page_address(const struct vm_area_struct *vma,
						const pgoff_t pgoff)
{
	const pgoff_t page_delta = pgoff - vma_start_pgoff(vma);
	const unsigned long offset = page_delta << PAGE_SHIFT;

	return vma->vm_start + offset;
}

This is one that I think makes more sense.

But in general, I'd rather hold off from yet more churn here.

I'm making these changes to establish a basis for virtual page offsets
introduced in [0], rather than just cleaning up in general.

These changes are really to make it such that we more consistently use these
forms, so when I introduce the virt pgoff versions, it fits canonically into
that.

And also beacuse I may as well improve kernel code as I go :)

But I think adding yet more doesn't really serve the same purpose.

But it's food for a follow up perhaps?

>
> >
> >  /**
> > @@ -1482,7 +1484,7 @@ static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
> >  		    file_inode(vma->vm_file) != uprobe->inode)
> >  			continue;
> >
> > -		offset = (loff_t)vma->vm_pgoff << PAGE_SHIFT;
> > +		offset = (loff_t)vma_start_pgoff(vma) << PAGE_SHIFT;
> >  		if (uprobe->offset <  offset ||
> >  		    uprobe->offset >= offset + vma->vm_end - vma->vm_start)
> >  			continue;
> > @@ -2453,7 +2455,8 @@ static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr)
> >  	if (!vm_file)
> >  		return NULL;
> >
> > -	offset = (loff_t)(vma->vm_pgoff << PAGE_SHIFT) + (bp_vaddr - vma->vm_start);
> > +	offset = (loff_t)(vma_start_pgoff(vma) << PAGE_SHIFT) +
> > +		(bp_vaddr - vma->vm_start);
>
> This is more extremely contrived logic that could be better expressed as
>
> loff_t vma_linear_off(vma, bp_vaddr);

See above.

>
> >  	uprobe = find_uprobe_rcu(vm_file->f_inode, offset);
> >  	if (!uprobe)
> >  		return NULL;
> > diff --git a/kernel/kcov.c b/kernel/kcov.c
> > index 1df373fb562b..b19b473c366a 100644
> > --- a/kernel/kcov.c
> > +++ b/kernel/kcov.c
> > @@ -512,7 +512,7 @@ static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
> >
> >  	spin_lock_irqsave(&kcov->lock, flags);
> >  	size = kcov->size * sizeof(unsigned long);
> > -	if (kcov->area == NULL || vma->vm_pgoff != 0 ||
> > +	if (kcov->area == NULL || vma_start_pgoff(vma) ||
>
> as a nit, perhaps                 vma_start_pgoff(vma) > 0
> would be a little more idiomatic.

I felt the if (<val>) form was more idiomatic?

>
> >  	    vma->vm_end - vma->vm_start != size) {
> >  		res = -EINVAL;
> >  		goto exit;
> > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> > index 56a328e94395..dfa493d54ef9 100644
> > --- a/kernel/trace/ring_buffer.c
> > +++ b/kernel/trace/ring_buffer.c
> > @@ -7613,7 +7613,8 @@ static int __rb_inc_dec_mapped(struct ring_buffer_per_cpu *cpu_buffer,
> >  static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
> >  			struct vm_area_struct *vma)
> >  {
> > -	unsigned long nr_subbufs, nr_pages, nr_vma_pages, pgoff = vma->vm_pgoff;
> > +	unsigned long nr_subbufs, nr_pages, nr_vma_pages;
> > +	pgoff_t pgoff = vma_start_pgoff(vma);
> >  	unsigned int subbuf_pages, subbuf_order;
> >  	struct page **pages __free(kfree) = NULL;
> >  	int p = 0, s = 0;
>
> Anyway, in general:
>
> Acked-by: Pedro Falcato <pfalcato@suse.de>

Thanks!

>
> --
> Pedro

[0]:https://lore.kernel.org/linux-mm/cover.1782745153.git.ljs@kernel.org/