On Mon, Sep 15, 2025 at 09:16:17AM -0300, Jason Gunthorpe wrote:
> On Wed, Sep 10, 2025 at 09:22:11PM +0100, Lorenzo Stoakes wrote:
> > +static int kcov_mmap_prepare(struct vm_area_desc *desc)
> > {
> > int res = 0;
> > - struct kcov *kcov = vma->vm_file->private_data;
> > - unsigned long size, off;
> > - struct page *page;
> > + struct kcov *kcov = desc->file->private_data;
> > + unsigned long size, nr_pages, i;
> > + struct page **pages;
> > unsigned long flags;
> >
> > spin_lock_irqsave(&kcov->lock, flags);
> > size = kcov->size * sizeof(unsigned long);
> > - if (kcov->area == NULL || vma->vm_pgoff != 0 ||
> > - vma->vm_end - vma->vm_start != size) {
> > + if (kcov->area == NULL || desc->pgoff != 0 ||
> > + vma_desc_size(desc) != size) {
>
> IMHO these range checks should be cleaned up into a helper:
>
> /* Returns true if the VMA falls within starting_pgoff to
> starting_pgoff + ROUND_DOWN(length_bytes, PAGE_SIZE))
> Is careful to avoid any arithmetic overflow.
> */
Right, but I can't refactor every driver I touch, it's not really tractable. I'd
like to get this change done before I retire :)
> vma_desc_check_range(desc, starting_pgoff=0, length_bytes=size);
>
> > + desc->vm_flags |= VM_DONTEXPAND;
> > + nr_pages = size >> PAGE_SHIFT;
> > +
> > + pages = mmap_action_mixedmap_pages(&desc->action, desc->start,
> > + nr_pages);
> > + if (!pages)
> > + return -ENOMEM;
> > +
> > + for (i = 0; i < nr_pages; i++)
> > + pages[i] = vmalloc_to_page(kcov->area + i * PAGE_SIZE);
>
> This is not a mixed map.
>
> All the memory comes from vmalloc_user() which makes them normal
> struct pages with refcounts.
>
> If anything the action should be called mmap_action_vmalloc_user() to
> match how the memory was allocated instead of open coding something.
Again we're getting into the same issue - my workload doesn't really permit
me to refactor every user of .mmap beyond converting sensibly to the new
scheme.
I think this kind of change is out of scope for the series.
I'd rather make this as apples-to-apples as possible for now so it can be
done vaguely mechanically.
Of course we can follow up with improvements later.
>
> Jason
Cheers, Lorenzo
