mm/gup: remove the vma allocation from gup_longterm_locked()

Long ago there wasn't a FOLL_LONGTERM flag so this DAX check was done by
post-processing the VMA list.

These days it is trivial to just check each VMA to see if it is DAX before
processing it inside __get_user_pages() and return failure if a DAX VMA is
encountered with FOLL_LONGTERM.

Removing the allocation of the VMA list is a significant speed up for many
call sites.

Add an IS_ENABLED to vma_is_fsdax so that code generation is unchanged
when DAX is compiled out.

Remove the dummy version of __gup_longterm_locked() as !CONFIG_CMA already
makes memalloc_nocma_save(), check_and_migrate_cma_pages(), and
memalloc_nocma_restore() into a NOP.

Link: https://lkml.kernel.org/r/0-v1-5551df3ed12e+b8-gup_dax_speedup_jgg@nvidia.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/fs.h

@@ -3230,7 +3230,7 @@ static inline bool vma_is_fsdax(struct vm_area_struct *vma)
 {
 	struct inode *inode;
 
-	if (!vma->vm_file)
+	if (!IS_ENABLED(CONFIG_FS_DAX) || !vma->vm_file)
 		return false;
 	if (!vma_is_dax(vma))
 		return false;

mm/gup.c

@@ -923,6 +923,9 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 	if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
 		return -EFAULT;
 
+	if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma))
+		return -EOPNOTSUPP;
+
 	if (write) {
 		if (!(vm_flags & VM_WRITE)) {
 			if (!(gup_flags & FOLL_FORCE))
@@ -1060,10 +1063,14 @@ static long __get_user_pages(struct mm_struct *mm,
 				goto next_page;
 			}
 
-			if (!vma || check_vma_flags(vma, gup_flags)) {
+			if (!vma) {
 				ret = -EFAULT;
 				goto out;
 			}
+			ret = check_vma_flags(vma, gup_flags);
+			if (ret)
+				goto out;
+
 			if (is_vm_hugetlb_page(vma)) {
 				i = follow_hugetlb_page(mm, vma, pages, vmas,
 						&start, &nr_pages, i,
@@ -1567,26 +1574,6 @@ struct page *get_dump_page(unsigned long addr)
 }
 #endif /* CONFIG_ELF_CORE */
 
-#if defined(CONFIG_FS_DAX) || defined (CONFIG_CMA)
-static bool check_dax_vmas(struct vm_area_struct **vmas, long nr_pages)
-{
-	long i;
-	struct vm_area_struct *vma_prev = NULL;
-
-	for (i = 0; i < nr_pages; i++) {
-		struct vm_area_struct *vma = vmas[i];
-
-		if (vma == vma_prev)
-			continue;
-
-		vma_prev = vma;
-
-		if (vma_is_fsdax(vma))
-			return true;
-	}
-	return false;
-}
-
 #ifdef CONFIG_CMA
 static long check_and_migrate_cma_pages(struct mm_struct *mm,
 					unsigned long start,
@@ -1705,63 +1692,23 @@ static long __gup_longterm_locked(struct mm_struct *mm,
 				  struct vm_area_struct **vmas,
 				  unsigned int gup_flags)
 {
-	struct vm_area_struct **vmas_tmp = vmas;
 	unsigned long flags = 0;
-	long rc, i;
+	long rc;
 
-	if (gup_flags & FOLL_LONGTERM) {
+	if (gup_flags & FOLL_LONGTERM)
-		if (!pages)
-			return -EINVAL;
-
-		if (!vmas_tmp) {
-			vmas_tmp = kcalloc(nr_pages,
-					   sizeof(struct vm_area_struct *),
-					   GFP_KERNEL);
-			if (!vmas_tmp)
-				return -ENOMEM;
-		}
 		flags = memalloc_nocma_save();
-	}
 
-	rc = __get_user_pages_locked(mm, start, nr_pages, pages,
+	rc = __get_user_pages_locked(mm, start, nr_pages, pages, vmas, NULL,
-				     vmas_tmp, NULL, gup_flags);
+				     gup_flags);
 
 	if (gup_flags & FOLL_LONGTERM) {
-		if (rc < 0)
+		if (rc > 0)
-			goto out;
+			rc = check_and_migrate_cma_pages(mm, start, rc, pages,
-
+							 vmas, gup_flags);
-		if (check_dax_vmas(vmas_tmp, rc)) {
-			if (gup_flags & FOLL_PIN)
-				unpin_user_pages(pages, rc);
-			else
-				for (i = 0; i < rc; i++)
-					put_page(pages[i]);
-			rc = -EOPNOTSUPP;
-			goto out;
-		}
-
-		rc = check_and_migrate_cma_pages(mm, start, rc, pages,
-						 vmas_tmp, gup_flags);
-out:
 		memalloc_nocma_restore(flags);
 	}
-
-	if (vmas_tmp != vmas)
-		kfree(vmas_tmp);
 	return rc;
 }
-#else /* !CONFIG_FS_DAX && !CONFIG_CMA */
-static __always_inline long __gup_longterm_locked(struct mm_struct *mm,
-						  unsigned long start,
-						  unsigned long nr_pages,
-						  struct page **pages,
-						  struct vm_area_struct **vmas,
-						  unsigned int flags)
-{
-	return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
-				       NULL, flags);
-}
-#endif /* CONFIG_FS_DAX || CONFIG_CMA */
 
 static bool is_valid_gup_flags(unsigned int gup_flags)
 {