[PATCH 4.9] cxl: Fix driver use count

[Andrew Donnellan]

From: Frederic Barrat <fbarrat at linux.vnet.ibm.com>

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 at linux.vnet.ibm.com>
Cc: stable at vger.kernel.org # v4.2+
Fixes: 7bb5d91a4dda ("cxl: Rework context lifetimes")
Acked-by: Andrew Donnellan <andrew.donnellan at au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
[ajd: backport to stable v4.9 tree]
Signed-off-by: Andrew Donnellan <andrew.donnellan at au1.ibm.com>
---
 drivers/misc/cxl/api.c  | 4 ++++
 drivers/misc/cxl/file.c | 8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/cxl/api.c b/drivers/misc/cxl/api.c
index 2e5233b60971..ae856161faa9 100644
--- a/drivers/misc/cxl/api.c
+++ b/drivers/misc/cxl/api.c
@@ -244,6 +244,10 @@ int cxl_start_context(struct cxl_context *ctx, u64 wed,
 		ctx->real_mode = false;
 	}
 
+	/*
+	 * Increment driver use count. Enables global TLBIs for hash
+	 * and callbacks to handle the segment table
+	 */
 	cxl_ctx_get();
 
 	if ((rc = cxl_ops->attach_process(ctx, kernel, wed, 0))) {
diff --git a/drivers/misc/cxl/file.c b/drivers/misc/cxl/file.c
index afa211397048..d3e009438991 100644
--- a/drivers/misc/cxl/file.c
+++ b/drivers/misc/cxl/file.c
@@ -91,7 +91,6 @@ static int __afu_open(struct inode *inode, struct file *file, bool master)
 
 	pr_devel("afu_open pe: %i\n", ctx->pe);
 	file->private_data = ctx;
-	cxl_ctx_get();
 
 	/* indicate success */
 	rc = 0;
@@ -213,6 +212,12 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
 	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_ops->attach_process(ctx, false, work.work_element_descriptor,
@@ -222,6 +227,7 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
 		put_pid(ctx->glpid);
 		put_pid(ctx->pid);
 		ctx->glpid = ctx->pid = NULL;
+		cxl_ctx_put();
 		goto out;
 	}
 
-- 
2.11.0