[PATCH 2/6] vfio/type1: drop mmap_sem now that locked_vm is atomic

[Daniel Jordan]

With locked_vm now an atomic, there is no need to take mmap_sem as
writer.  Delete and refactor accordingly.

Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: <linux-mm@xxxxxxxxx>
Cc: <kvm@xxxxxxxxxxxxxxx>
Cc: <linux-kernel@xxxxxxxxxxxxxxx>
---
 drivers/vfio/vfio_iommu_type1.c | 27 +++++++++------------------
 1 file changed, 9 insertions(+), 18 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 5b2878697286..a227de6d9c4c 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -257,7 +257,8 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn)
 static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
 {
 	struct mm_struct *mm;
-	int ret;
+	s64 locked_vm;
+	int ret = 0;
 
 	if (!npage)
 		return 0;
@@ -266,25 +267,15 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
 	if (!mm)
 		return -ESRCH; /* process exited */
 
-	ret = down_write_killable(&mm->mmap_sem);
-	if (!ret) {
-		if (npage > 0) {
-			if (!dma->lock_cap) {
-				s64 locked_vm = atomic64_read(&mm->locked_vm);
-				unsigned long limit;
-
-				limit = task_rlimit(dma->task,
-						RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+	locked_vm = atomic64_add_return(npage, &mm->locked_vm);
 
-				if (locked_vm + npage > limit)
-					ret = -ENOMEM;
-			}
+	if (npage > 0 && !dma->lock_cap) {
+		unsigned long limit = task_rlimit(dma->task, RLIMIT_MEMLOCK) >>
+								   PAGE_SHIFT;
+		if (locked_vm > limit) {
+			atomic64_sub(npage, &mm->locked_vm);
+			ret = -ENOMEM;
 		}
-
-		if (!ret)
-			atomic64_add(npage, &mm->locked_vm);
-
-		up_write(&mm->mmap_sem);
 	}
 
 	if (async)
-- 
2.21.0