vfio/type1: Catch zero from pin_user_pages_remote()

jira LE-3557
Rebuild_History Non-Buildable kernel-5.14.0-570.26.1.el9_6
commit-author Alex Williamson <[email protected]>
commit afe84f3

pin_user_pages_remote() can currently return zero for invalid args
or zero nr_pages, neither of which should ever happen.  However
vaddr_get_pfns() indicates it should only ever return a positive
value or -errno and there's a theoretical case where this can slip
through and be unhandled by callers.  Therefore convert zero to
-EFAULT.

	Reviewed-by: Peter Xu <[email protected]>
	Reviewed-by: Mitchell Augustin <[email protected]>
	Tested-by: Mitchell Augustin <[email protected]>
	Reviewed-by: Jason Gunthorpe <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
	Signed-off-by: Alex Williamson <[email protected]>
(cherry picked from commit afe84f3)
	Signed-off-by: Jonathan Maple <[email protected]>

Author: PlaidCat

drivers/vfio/vfio_iommu_type1.c

@@ -571,6 +571,8 @@ static int vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
 	if (ret > 0) {
 		*pfn = page_to_pfn(pages[0]);
 		goto done;
+	} else if (!ret) {
+		ret = -EFAULT;
 	}
 
 	vaddr = untagged_addr_remote(mm, vaddr);