linux-kernel - Re: [PATCH 2/4 v5] cxl/core: Add helpers to detect Low Memory Holes on x86

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Message-ID: <d3d1757a-20b1-49e4-90fe-8a1751c40c59@intel.com>
Date: Wed, 5 Nov 2025 11:51:54 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
 linux-cxl@...r.kernel.org, kernel test robot <lkp@...el.com>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
 Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>,
 Dan Williams <dan.j.williams@...el.com>, Jonathan Corbet <corbet@....net>,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 Gregory Price <gourry@...rry.net>, Robert Richter <rrichter@....com>,
 Cheatham Benjamin <benjamin.cheatham@....com>
Subject: Re: [PATCH 2/4 v5] cxl/core: Add helpers to detect Low Memory Holes
 on x86



On 11/5/25 11:20 AM, Fabio M. De Francesco wrote:
> On Friday, October 10, 2025 4:49:01 PM Central European Standard Time kernel test robot wrote:
>> Hi Fabio,
>>
>> kernel test robot noticed the following build warnings:
>>
>> [auto build test WARNING on 46037455cbb748c5e85071c95f2244e81986eb58]
>>
>> url:    https://github.com/intel-lab-lkp/linux/commits/Fabio-M-De-Francesco/cxl-core-Change-match_-_by_range-signatures/20251010-111627
>> base:   46037455cbb748c5e85071c95f2244e81986eb58
>> patch link:    https://lore.kernel.org/r/20251006155836.791418-3-fabio.m.de.francesco%40linux.intel.com
>> patch subject: [PATCH 2/4 v5] cxl/core: Add helpers to detect Low Memory Holes on x86
>> config: i386-randconfig-011-20251010 (https://download.01.org/0day-ci/archive/20251010/202510102229.iFcGqbMH-lkp@intel.com/config)
>> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251010/202510102229.iFcGqbMH-lkp@intel.com/reproduce)
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@...el.com>
>> | Closes: https://lore.kernel.org/oe-kbuild-all/202510102229.iFcGqbMH-lkp@intel.com/
>>
>> All warnings (new ones prefixed by >>):
>>
>>>> drivers/cxl/core/platform_quirks.c:70:36: warning: result of comparison of constant 4294967296 with expression of type 'const resource_size_t' (aka 'const unsigned int') is always true [-Wtautological-constant-out-of-range-compare]
>>       70 |             res->end < r->end && res->end < (LMH_CFMWS_RANGE_START + SZ_4G) &&
>>          |                                  ~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>    1 warning generated.
>>
> Unavoidable warning wherever res->end is an u32 variable:
> 
> /* include/linux/types.h */
> 
> #ifdef CONFIG_PHYS_ADDR_T_64BIT
> typedef u64 phys_addr_t;
> #else
> typedef u32 phys_addr_t;
> #endif
> 
> typedef phys_addr_t resource_size_t;
> 
> /* include/linux/ioport.h */
> 
> struct resource {
> 	resource_size_t start;
> 	resource_size_t end;
> };
> 
> I think we should ignore this report.

Maybe try casting res->end to (u64) and see if it shuts the warning up?

DJ

> 
> Fabio
>>
>> vim +70 drivers/cxl/core/platform_quirks.c
>>
>>     50	
>>     51	/**
>>     52	 * platform_region_matches_cxld() - Platform quirk to match a CXL Region and a
>>     53	 * Switch or Endpoint Decoder. It allows matching on platforms with LMH's.
>>     54	 * @p: Region Params against which @cxled is matched.
>>     55	 * @cxld: Switch or Endpoint Decoder to be tested for matching @p.
>>     56	 *
>>     57	 * Similar to platform_cxlrd_matches_cxled(), it matches regions and
>>     58	 * decoders on platforms with LMH's.
>>     59	 *
>>     60	 * Return: true if a Decoder matches a Region, else false.
>>     61	 */
>>     62	bool platform_region_matches_cxld(const struct cxl_region_params *p,
>>     63					  const struct cxl_decoder *cxld)
>>     64	{
>>     65		const struct range *r = &cxld->hpa_range;
>>     66		const struct resource *res = p->res;
>>     67		int align = cxld->interleave_ways * SZ_256M;
>>     68	
>>     69		if (res->start == LMH_CFMWS_RANGE_START && res->start == r->start &&
>>   > 70		    res->end < r->end && res->end < (LMH_CFMWS_RANGE_START + SZ_4G) &&
>>     71		    IS_ALIGNED(range_len(r), align))
>>     72			return true;
>>     73	
>>     74		return false;
>>     75	}
>>     76	
>>
>> -- 
>> 0-DAY CI Kernel Test Service
>> https://github.com/intel/lkp-tests/wiki
>>
>>
> 
> 
> 
>