vfio/type1: track locked_vm per dma

Track locked_vm per dma struct, and create a new subroutine, both for use
in a subsequent patch.  No functional change.

Fixes: c3cbab24db ("vfio/type1: implement interfaces to update vaddr")
Cc: stable@vger.kernel.org
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/1675184289-267876-4-git-send-email-steven.sistare@oracle.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio_iommu_type1.c

@@ -101,6 +101,7 @@ struct vfio_dma {
 	struct rb_root		pfn_list;	/* Ex-user pinned pfn list */
 	unsigned long		*bitmap;
 	struct mm_struct	*mm;
+	size_t			locked_vm;
 };
 
 struct vfio_batch {
@@ -413,6 +414,19 @@ static int vfio_iova_put_vfio_pfn(struct vfio_dma *dma, struct vfio_pfn *vpfn)
 	return ret;
 }
 
+static int mm_lock_acct(struct task_struct *task, struct mm_struct *mm,
+			bool lock_cap, long npage)
+{
+	int ret = mmap_write_lock_killable(mm);
+
+	if (ret)
+		return ret;
+
+	ret = __account_locked_vm(mm, abs(npage), npage > 0, task, lock_cap);
+	mmap_write_unlock(mm);
+	return ret;
+}
+
 static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
 {
 	struct mm_struct *mm;
@@ -425,12 +439,9 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
 	if (async && !mmget_not_zero(mm))
 		return -ESRCH; /* process exited */
 
-	ret = mmap_write_lock_killable(mm);
-	if (!ret) {
-		ret = __account_locked_vm(mm, abs(npage), npage > 0, dma->task,
-					  dma->lock_cap);
-		mmap_write_unlock(mm);
-	}
+	ret = mm_lock_acct(dma->task, mm, dma->lock_cap, npage);
+	if (!ret)
+		dma->locked_vm += npage;
 
 	if (async)
 		mmput(mm);