diff mbox series

[v2,2/3] cxl: Fix driver use count

Message ID 20170830101550.16821-2-fbarrat@linux.vnet.ibm.com (mailing list archive)
State Accepted
Commit 197267d0356004a31c4d6b6336598f5dff3301e1
Headers show
Series [v2,1/3] powerpc/mm: Export flush_all_mm() | expand

Commit Message

Frederic Barrat Aug. 30, 2017, 10:15 a.m. UTC 
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@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org # v4.2+
Fixes: 7bb5d91a4dda ("cxl: Rework context lifetimes")
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
---
Changelog:
v2: fix typo in comments (Thanks to Andrew)

 drivers/misc/cxl/api.c  | 4 ++++
 drivers/misc/cxl/file.c | 8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

Comments

Michael Ellerman Aug. 30, 2017, 1:18 p.m. UTC | #1 
Frederic Barrat <fbarrat@linux.vnet.ibm.com> writes:

> 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@linux.vnet.ibm.com>
> Cc: stable@vger.kernel.org # v4.2+
> Fixes: 7bb5d91a4dda ("cxl: Rework context lifetimes")
> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>

I'll pick this up straight away, because it's a fix.

So you can drop this from the series.

cheers
Michael Ellerman Aug. 31, 2017, 11:36 a.m. UTC | #2 
On Wed, 2017-08-30 at 10:15:49 UTC, Frederic Barrat wrote:
> 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@linux.vnet.ibm.com>
> Cc: stable@vger.kernel.org # v4.2+
> Fixes: 7bb5d91a4dda ("cxl: Rework context lifetimes")
> Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/197267d0356004a31c4d6b6336598f

cheers
diff mbox series

Patch

diff --git a/drivers/misc/cxl/api.c b/drivers/misc/cxl/api.c
index 1a138c83f877..a0c44d16bf30 100644
--- a/drivers/misc/cxl/api.c
+++ b/drivers/misc/cxl/api.c
@@ -336,6 +336,10 @@  int cxl_start_context(struct cxl_context *ctx, u64 wed,
 			mmput(ctx->mm);
 	}
 
+	/*
+	 * 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 0761271d68c5..4bfad9f6dc9f 100644
--- a/drivers/misc/cxl/file.c
+++ b/drivers/misc/cxl/file.c
@@ -95,7 +95,6 @@  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;
@@ -225,6 +224,12 @@  static long afu_ioctl_start_work(struct cxl_context *ctx,
 	if (ctx->mm)
 		mmput(ctx->mm);
 
+	/*
+	 * 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,
@@ -233,6 +238,7 @@  static long afu_ioctl_start_work(struct cxl_context *ctx,
 		cxl_adapter_context_put(ctx->afu->adapter);
 		put_pid(ctx->pid);
 		ctx->pid = NULL;
+		cxl_ctx_put();
 		cxl_context_mm_count_put(ctx);
 		goto out;
 	}