[PATCH 4.4] cxl: Fix driver use count

[Greg KH]

On Wed, Sep 27, 2017 at 10:43:17AM +1000, Andrew Donnellan wrote:
> 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 v4.4 tree]
> Signed-off-by: Andrew Donnellan <andrew.donnellan at au1.ibm.com>

Thanks for this and the 4.9 backport.

greg k-h