On Thu, Jan 30, 2025 at 04:57:39PM +1100, Alistair Popple wrote:
> On Wed, Jan 29, 2025 at 12:54:01PM +0100, David Hildenbrand wrote:
[...]
> > -int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
> > - unsigned long end, struct page **pages,
> > - void *owner)
> > +struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr,
> > + void *owner, struct folio **foliop)
> > {
> > - long npages = (end - start) >> PAGE_SHIFT;
> > - long i;
> > + struct folio *folio;
> > + struct page *page;
> > + long npages;
> > +
> > + mmap_assert_locked(mm);
> >
> > - npages = get_user_pages_remote(mm, start, npages,
> > + /*
> > + * Fault in the page writable and try to lock it; note that if the
> > + * address would already be marked for exclusive use by the device,
> > + * the GUP call would undo that first by triggering a fault.
> > + */
> > + npages = get_user_pages_remote(mm, addr, 1,
> > FOLL_GET | FOLL_WRITE | FOLL_SPLIT_PMD,
> > - pages, NULL);
> > - if (npages < 0)
> > - return npages;
> > -
> > - for (i = 0; i < npages; i++, start += PAGE_SIZE) {
> > - struct folio *folio = page_folio(pages[i]);
> > - if (PageTail(pages[i]) || !folio_trylock(folio)) {
> > - folio_put(folio);
> > - pages[i] = NULL;
> > - continue;
> > - }
> > + &page, NULL);
> > + if (npages != 1)
> > + return ERR_PTR(npages);
> > + folio = page_folio(page);
> >
> > - if (!folio_make_device_exclusive(folio, mm, start, owner)) {
> > - folio_unlock(folio);
> > - folio_put(folio);
> > - pages[i] = NULL;
> > - }
> > + if (!folio_test_anon(folio) || folio_test_hugetlb(folio)) {
> > + folio_put(folio);
> > + return ERR_PTR(-EOPNOTSUPP);
> > + }
> > +
> > + if (!folio_trylock(folio)) {
Actually I think we can make this folio_lock(folio) now. The only reason for
the trylock was to avoid deadlock between other threads looping over a range
of folios while holding folio locks which is something the migration code also
does.
- Alistair
> > + folio_put(folio);
> > + return ERR_PTR(-EBUSY);
> > }
> >
> > - return npages;
> > + if (!folio_make_device_exclusive(folio, mm, addr, owner)) {
> > + folio_unlock(folio);
> > + folio_put(folio);
> > + return ERR_PTR(-EBUSY);
> > + }
> > + *foliop = folio;
> > + return page;
> > }
> > -EXPORT_SYMBOL_GPL(make_device_exclusive_range);
> > +EXPORT_SYMBOL_GPL(make_device_exclusive);
> > #endif
> >
> > void __put_anon_vma(struct anon_vma *anon_vma)
> > --
> > 2.48.1
> >
>
