[PATCH v2 5/7] io_uring: rsrc: use FOLL_SAME_FILE on pin_user_pages()

[Lorenzo Stoakes <lstoakes@gmail.com>]

Commit edd478269640 ("io_uring/rsrc: disallow multi-source reg buffers")
prevents io_pin_pages() from pinning pages spanning multiple VMAs with
permitted characteristics (anon/huge), requiring that all VMAs share the
same vm_file.

The newly introduced FOLL_SAME_FILE flag permits this to be expressed as a
GUP flag rather than having to retrieve VMAs to perform the check.

We then only need to perform a VMA lookup for the first VMA to assert the
anon/hugepage requirement as we know the rest of the VMAs will possess the
same characteristics.

Doing this eliminates the one instance of vmas being used by
pin_user_pages().

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 io_uring/rsrc.c | 39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 7a43aed8e395..adc860bcbd4f 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1141,9 +1141,8 @@ static int io_buffer_account_pin(struct io_ring_ctx *ctx, struct page **pages,
 struct page **io_pin_pages(unsigned long ubuf, unsigned long len, int *npages)
 {
 	unsigned long start, end, nr_pages;
-	struct vm_area_struct **vmas = NULL;
 	struct page **pages = NULL;
-	int i, pret, ret = -ENOMEM;
+	int pret, ret = -ENOMEM;
 
 	end = (ubuf + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	start = ubuf >> PAGE_SHIFT;
@@ -1153,31 +1152,26 @@ struct page **io_pin_pages(unsigned long ubuf, unsigned long len, int *npages)
 	if (!pages)
 		goto done;
 
-	vmas = kvmalloc_array(nr_pages, sizeof(struct vm_area_struct *),
-			      GFP_KERNEL);
-	if (!vmas)
-		goto done;
-
 	ret = 0;
 	mmap_read_lock(current->mm);
-	pret = pin_user_pages(ubuf, nr_pages, FOLL_WRITE | FOLL_LONGTERM,
-			      pages, vmas);
+
+	pret = pin_user_pages(ubuf, nr_pages,
+			      FOLL_WRITE | FOLL_LONGTERM | FOLL_SAME_FILE,
+			      pages, NULL);
 	if (pret == nr_pages) {
-		struct file *file = vmas[0]->vm_file;
+		/*
+		 * lookup the first VMA, we require that all VMAs in range
+		 * maintain the same file characteristics, as enforced by
+		 * FOLL_SAME_FILE
+		 */
+		struct vm_area_struct *vma = vma_lookup(current->mm, ubuf);
+		struct file *file;
 
 		/* don't support file backed memory */
-		for (i = 0; i < nr_pages; i++) {
-			if (vmas[i]->vm_file != file) {
-				ret = -EINVAL;
-				break;
-			}
-			if (!file)
-				continue;
-			if (!vma_is_shmem(vmas[i]) && !is_file_hugepages(file)) {
-				ret = -EOPNOTSUPP;
-				break;
-			}
-		}
+		file = vma->vm_file;
+		if (file && !vma_is_shmem(vma) && !is_file_hugepages(file))
+			ret = -EOPNOTSUPP;
+
 		*npages = nr_pages;
 	} else {
 		ret = pret < 0 ? pret : -EFAULT;
@@ -1194,7 +1188,6 @@ struct page **io_pin_pages(unsigned long ubuf, unsigned long len, int *npages)
 	}
 	ret = 0;
 done:
-	kvfree(vmas);
 	if (ret < 0) {
 		kvfree(pages);
 		pages = ERR_PTR(ret);
-- 
2.40.0