Re: [PATCH] cxl/region: Fix null pointer dereference due to pass through decoder commit

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Thu, 2022-08-18 at 17:42 +0100, Jonathan Cameron wrote:
> Not all decoders have a commit callback.
> 
> The CXL specification allows a host bridge with a single root port to
> have no explicit HDM decoders. Currently we assumes there are none.

s/assumes/assume/ or,
'the region driver' instead of 'we'?

> As such we create a special pass through decoder instance without
> a commit callback.
> 
> Prior to this patch, the commit callback was called unconditionally.
> Thus a configuration with 1 Host Bridge, 1 Root Port, 1 switch with
> multiple downstream ports below which there are multiple CXL type 3
> devices results in a situation where committing the region causes
> a null pointer dereference.
> 
> Reported-by: Bobo WL <lmw.bobo@gmail.com>
> Fixes: 176baefb2eb5 ("cxl/hdm: Commit decoder state to hardware")
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
> 
> We could fix this with a stub function perhaps as an alternative?
> 
>  drivers/cxl/core/region.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Other than that, looks good to me,

Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>

> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 401148016978..c49d9a5f1091 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -174,7 +174,8 @@ static int cxl_region_decode_commit(struct
> cxl_region *cxlr)
>                      iter = to_cxl_port(iter->dev.parent)) {
>                         cxl_rr = cxl_rr_load(iter, cxlr);
>                         cxld = cxl_rr->decoder;
> -                       rc = cxld->commit(cxld);
> +                       if (cxld->commit)
> +                               rc = cxld->commit(cxld);
>                         if (rc)
>                                 break;
>                 }