Re: [PATCH] ocxl: Fix endiannes bug in ocxl_link_update_pe()

[Greg Kurz <groug@kaod.org>]

On Mon, 17 Dec 2018 11:38:51 +1100
"Alastair D'Silva" <alastair@au1.ibm.com> wrote:

> On Sun, 2018-12-16 at 22:28 +0100, Greg Kurz wrote:
> > All fields in the PE are big-endian. Use cpu_to_be32() like
> > everywhere
> > else something is written to the PE. Otherwise a wrong TID will be
> > used
> > by the NPU. If this TID happens to point to an existing thread
> > sharing
> > the same mm, it could be woken up by error. This is highly improbable
> > though. The likely outcome of this is the NPU not finding the target
> > thread and forcing the AFU into sending an interrupt, which userspace
> > is supposed to handle anyway.
> > 
> > Fixes: e948e06fc63a ("ocxl: Expose the thread_id needed for wait on
> > POWER9")
> > Cc: stable@vger.kernel.org      # v4.18
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> > 
> > This bug remained unnoticed so far because the current OCXL test
> > suite
> > happens to call OCXL_IOCTL_ENABLE_P9_WAIT before attaching a context.
> > This causes ocxl_link_update_pe() to be called before
> > ocxl_link_add_pe()
> > which re-writes the TID in the PE with the appropriate endianness.
> > 
> > I have some patches that change the behavior of the OCXL test suite
> > so that
> > it can catch the issue:
> > 
> > https://github.com/gkurz/libocxl/commits/wake-host-thread-rework
> > ---
> >  drivers/misc/ocxl/link.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/misc/ocxl/link.c b/drivers/misc/ocxl/link.c
> > index 31695a078485..646d16450066 100644
> > --- a/drivers/misc/ocxl/link.c
> > +++ b/drivers/misc/ocxl/link.c
> > @@ -566,7 +566,7 @@ int ocxl_link_update_pe(void *link_handle, int
> > pasid, __u16 tid)
> >  
> >  	mutex_lock(&spa->spa_lock);
> >  
> > -	pe->tid = tid;
> > +	pe->tid = cpu_to_be32(tid);
> >  
> >  	/*
> >  	 * The barrier makes sure the PE is updated
> >   
> 
> Good catch, thanks.
> 
> Reviewed-by: Alastair D'Silva <alastair@d-silva.org>
> 

Friendly ping before Xmas break :)