Commit 5b992412 authored by Alex Williamson's avatar Alex Williamson
Browse files

Revert "vfio/type1: Unpin zero pages" 



This reverts commit 873aefb3.

This was a heinous workaround and it turns out it's been fixed in mm
twice since it was introduced.  Most recently, commit c8070b78
("mm: Don't pin ZERO_PAGE in pin_user_pages()") would have prevented
running up the zeropage refcount, but even before that commit
84209e87 ("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: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarKevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240229223544.257207-1-alex.williamson@redhat.com


Signed-off-by: default avatarAlex Williamson <alex.williamson@redhat.com>
parent 81617c17

drivers/vfio/vfio_iommu_type1.c

+0 −12
Original line number Diff line number Diff line
@@ -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;

	}