[PATCH 4.4 35/41] cxl: Fix driver use count

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Frederic Barrat <fbarrat@xxxxxxxxxxxxxxxxxx>

commit 197267d0356004a31c4d6b6336598f5dff3301e1 upstream.

cxl keeps a driver use count, which is used with the hash memory model
on p8 to know when to upgrade local TLBIs to global and to trigger
callbacks to manage the MMU for PSL8.

If a process opens a context and closes without attaching or fails the
attachment, the driver use count is never decremented. As a
consequence, TLB invalidations remain global, even if there are no
active cxl contexts.

We should increment the driver use count when the process is attaching
to the cxl adapter, and not on open. It's not needed before the
adapter starts using the context and the use count is decremented on
the detach path, so it makes more sense.

It affects only the user api. The kernel api is already doing The
Right Thing.

Signed-off-by: Frederic Barrat <fbarrat@xxxxxxxxxxxxxxxxxx>
Fixes: 7bb5d91a4dda ("cxl: Rework context lifetimes")
Acked-by: Andrew Donnellan <andrew.donnellan@xxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
[ajd: backport to stable v4.4 tree]
Signed-off-by: Andrew Donnellan <andrew.donnellan@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/misc/cxl/api.c  |    4 ++++
 drivers/misc/cxl/file.c |    8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/misc/cxl/api.c
+++ b/drivers/misc/cxl/api.c
@@ -176,6 +176,10 @@ int cxl_start_context(struct cxl_context
 		kernel = false;
 	}
 
+	/*
+	 * Increment driver use count. Enables global TLBIs for hash
+	 * and callbacks to handle the segment table
+	 */
 	cxl_ctx_get();
 
 	if ((rc = cxl_attach_process(ctx, kernel, wed , 0))) {
--- a/drivers/misc/cxl/file.c
+++ b/drivers/misc/cxl/file.c
@@ -94,7 +94,6 @@ static int __afu_open(struct inode *inod
 
 	pr_devel("afu_open pe: %i\n", ctx->pe);
 	file->private_data = ctx;
-	cxl_ctx_get();
 
 	/* indicate success */
 	rc = 0;
@@ -205,11 +204,18 @@ static long afu_ioctl_start_work(struct
 	ctx->pid = get_task_pid(current, PIDTYPE_PID);
 	ctx->glpid = get_task_pid(current->group_leader, PIDTYPE_PID);
 
+	/*
+	 * Increment driver use count. Enables global TLBIs for hash
+	 * and callbacks to handle the segment table
+	 */
+	cxl_ctx_get();
+
 	trace_cxl_attach(ctx, work.work_element_descriptor, work.num_interrupts, amr);
 
 	if ((rc = cxl_attach_process(ctx, false, work.work_element_descriptor,
 				     amr))) {
 		afu_release_irqs(ctx, ctx);
+		cxl_ctx_put();
 		goto out;
 	}