Revert "vfio/type1: Unpin zero pages"

This reverts commit 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4.

This was a heinous workaround and it turns out it's been fixed in mm
twice since it was introduced.  Most recently, commit c8070b787519
("mm: Don't pin ZERO_PAGE in pin_user_pages()") would have prevented
running up the zeropage refcount, but even before that commit
84209e87c696 ("mm/gup: reliable R/O long-term pinning in COW mappings")
avoids the vfio use case from pinning the zeropage at all, instead
replacing it with exclusive anonymous pages.

Remove this now useless overhead.

Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240229223544.257207-1-alex.williamson@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index b2854d7939ce02ddf2be186e483c0f8c3f094a26..b5c15fe8f9fcf91911dcb391031713e517588297 100644 (file)
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -567,18 +567,6 @@ static int vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
        ret = pin_user_pages_remote(mm, vaddr, npages, flags | FOLL_LONGTERM,
                                    pages, NULL);
        if (ret > 0) {
-               int i;
-
-               /*
-                * The zero page is always resident, we don't need to pin it
-                * and it falls into our invalid/reserved test so we don't
-                * unpin in put_pfn().  Unpin all zero pages in the batch here.
-                */
-               for (i = 0 ; i < ret; i++) {
-                       if (unlikely(is_zero_pfn(page_to_pfn(pages[i]))))
-                               unpin_user_page(pages[i]);
-               }
-
                *pfn = page_to_pfn(pages[0]);
                goto done;
        }