Re: [PATCH 3/4] cxl: Add extended linear cache address alias emission for cxl events

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Wed, 4 Dec 2024 15:46:48 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> Add the aliased address of extended linear cache when emitting event
> trace for DRAM and general media of CXL events.
> 
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
I wonder if you want to future proof the hpa_alias for potential case
of there being more than 1?  hpa_alias0 or similar so that we can add
more as needed?


Otherwise, looks like there is either a null point dereference or
overly paranoid existing code. I haven't checked which but changes
needed either way.

Jonathan

> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 5175138c4fb7..4017b7afa78a 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -856,6 +856,24 @@ int cxl_enumerate_cmds(struct cxl_memdev_state *mds)
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_enumerate_cmds, CXL);
>  
> +static u64 cxlr_hpa_cache_alias(struct cxl_region *cxlr, u64 hpa)
> +{
> +	struct cxl_region_params *p = &cxlr->params;

Bad idea to unconditionally dereference I think. See below.

> +	int nid;
> +
> +	if (!p->cache_size)
> +		return ~0ULL;
> +
> +	nid = cxl_region_nid(cxlr);
> +	if (nid == NUMA_NO_NODE)
> +		nid = 0;
> +
> +	if (hpa >= p->res->start + p->cache_size)
> +		return hpa - p->cache_size;
> +
> +	return hpa + p->cache_size;
> +}
> +
>  void cxl_event_trace_record(const struct cxl_memdev *cxlmd,
>  			    enum cxl_event_log_type type,
>  			    enum cxl_event_type event_type,
> @@ -871,7 +889,7 @@ void cxl_event_trace_record(const struct cxl_memdev *cxlmd,
>  	}
>  
>  	if (trace_cxl_general_media_enabled() || trace_cxl_dram_enabled()) {
> -		u64 dpa, hpa = ULLONG_MAX;
> +		u64 dpa, hpa = ULLONG_MAX, hpa_alias;
>  		struct cxl_region *cxlr;
>  
>  		/*
> @@ -887,11 +905,14 @@ void cxl_event_trace_record(const struct cxl_memdev *cxlmd,
>  		if (cxlr)
>  			hpa = cxl_dpa_to_hpa(cxlr, cxlmd, dpa);
>  
> +		hpa_alias = cxlr_hpa_cache_alias(cxlr, hpa);

If there is no region, and hence no hpa does it make sense to call this?
Particularly as first thing done in this is to dereference cxlr.


> +
>  		if (event_type == CXL_CPER_EVENT_GEN_MEDIA)
>  			trace_cxl_general_media(cxlmd, type, cxlr, hpa,
> -						&evt->gen_media);
> +						hpa_alias, &evt->gen_media);
>  		else if (event_type == CXL_CPER_EVENT_DRAM)
> -			trace_cxl_dram(cxlmd, type, cxlr, hpa, &evt->dram);
> +			trace_cxl_dram(cxlmd, type, cxlr, hpa, hpa_alias,
> +				       &evt->dram);
>  	}
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_event_trace_record, CXL);