[PATCH 02/11] mm: call import_iovec() instead of rw_copy_check_uvector() in process_vm_rw()

[Christoph Hellwig <hch@xxxxxx>]

From: David Laight <David.Laight@xxxxxxxxxx>

This is the only direct call of rw_copy_check_uvector().  Removing it
will allow rw_copy_check_uvector() to be inlined into import_iovec(),
while only paying a minor price by setting up an otherwise unused
iov_iter in the process_vm_readv/process_vm_writev syscalls that aren't
in a super hot path.

Signed-off-by: David Laight <david.laight@xxxxxxxxxx>
[hch: expanded the commit log, pass CHECK_IOVEC_ONLY instead of 0 for the
      compat case, handle CHECK_IOVEC_ONLY in iov_iter_init]
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 lib/iov_iter.c         |  2 +-
 mm/process_vm_access.c | 33 ++++++++++++++++++---------------
 2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 5e40786c8f1232..db54588406dfae 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -443,7 +443,7 @@ void iov_iter_init(struct iov_iter *i, unsigned int direction,
 			const struct iovec *iov, unsigned long nr_segs,
 			size_t count)
 {
-	WARN_ON(direction & ~(READ | WRITE));
+	WARN_ON(direction & ~(READ | WRITE | CHECK_IOVEC_ONLY));
 	direction &= READ | WRITE;
 
 	/* It will get better.  Eventually... */
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index 29c052099affdc..40cd502c337534 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -264,7 +264,7 @@ static ssize_t process_vm_rw(pid_t pid,
 	struct iovec iovstack_r[UIO_FASTIOV];
 	struct iovec *iov_l = iovstack_l;
 	struct iovec *iov_r = iovstack_r;
-	struct iov_iter iter;
+	struct iov_iter iter_l, iter_r;
 	ssize_t rc;
 	int dir = vm_write ? WRITE : READ;
 
@@ -272,23 +272,25 @@ static ssize_t process_vm_rw(pid_t pid,
 		return -EINVAL;
 
 	/* Check iovecs */
-	rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
+	rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter_l);
 	if (rc < 0)
 		return rc;
-	if (!iov_iter_count(&iter))
+	if (!iov_iter_count(&iter_l))
 		goto free_iovecs;
 
-	rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
-				   iovstack_r, &iov_r);
+	rc = import_iovec(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV, &iov_r,
+			  &iter_r);
 	if (rc <= 0)
 		goto free_iovecs;
 
-	rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
+	rc = process_vm_rw_core(pid, &iter_l, iter_r.iov, iter_r.nr_segs,
+				flags, vm_write);
 
 free_iovecs:
 	if (iov_r != iovstack_r)
 		kfree(iov_r);
-	kfree(iov_l);
+	if (iov_l != iovstack_l)
+		kfree(iov_l);
 
 	return rc;
 }
@@ -322,30 +324,31 @@ compat_process_vm_rw(compat_pid_t pid,
 	struct iovec iovstack_r[UIO_FASTIOV];
 	struct iovec *iov_l = iovstack_l;
 	struct iovec *iov_r = iovstack_r;
-	struct iov_iter iter;
+	struct iov_iter iter_l, iter_r;
 	ssize_t rc = -EFAULT;
 	int dir = vm_write ? WRITE : READ;
 
 	if (flags != 0)
 		return -EINVAL;
 
-	rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
+	rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter_l);
 	if (rc < 0)
 		return rc;
-	if (!iov_iter_count(&iter))
+	if (!iov_iter_count(&iter_l))
 		goto free_iovecs;
-	rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
-					  UIO_FASTIOV, iovstack_r,
-					  &iov_r);
+	rc = compat_import_iovec(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
+				 &iov_r, &iter_r);
 	if (rc <= 0)
 		goto free_iovecs;
 
-	rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
+	rc = process_vm_rw_core(pid, &iter_l, iter_r.iov, iter_r.nr_segs,
+				flags, vm_write);
 
 free_iovecs:
 	if (iov_r != iovstack_r)
 		kfree(iov_r);
-	kfree(iov_l);
+	if (iov_l != iovstack_l)
+		kfree(iov_l);
 	return rc;
 }
 
-- 
2.28.0