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

[Dave Jiang <dave.jiang@intel.com>]

On 12/24/24 5:11 AM, Jonathan Cameron wrote:
> 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?

Do you mean when emitting via the trace? Yeah I can change it to hpa_alias0 in the output string.


> 
> 
> 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.

I'll move it under the if (cxlr) and also add a check for cxlr in the helper function.

DJ


> 
> 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);
>