linux-kernel - Re: [PATCH v4 1/2] KVM: guest_memfd: add generic population via write

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Message-ID: <8dd43501-80be-43bf-8eac-a4265e7595ea@amazon.com>
Date: Mon, 1 Sep 2025 15:29:59 +0100
From: Nikita Kalyazin <kalyazin@...zon.com>
To: David Hildenbrand <david@...hat.com>, kernel test robot <lkp@...el.com>,
	"Kalyazin, Nikita" <kalyazin@...zon.co.uk>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "shuah@...nel.org" <shuah@...nel.org>
CC: <llvm@...ts.linux.dev>, <oe-kbuild-all@...ts.linux.dev>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jthoughton@...gle.com" <jthoughton@...gle.com>, "Roy, Patrick"
	<roypat@...zon.co.uk>, "Thomson, Jack" <jackabt@...zon.co.uk>, "Manwaring,
 Derek" <derekmn@...zon.com>, "Cali, Marco" <xmarcalx@...zon.co.uk>
Subject: Re: [PATCH v4 1/2] KVM: guest_memfd: add generic population via write



On 01/09/2025 11:09, David Hildenbrand wrote:

> On 30.08.25 20:56, kernel test robot wrote:
>> Hi Nikita,
>>
>> kernel test robot noticed the following build errors:
>>
>> [auto build test ERROR on a6ad54137af92535cfe32e19e5f3bc1bb7dbd383]
>>
>> url:    https://github.com/intel-lab-lkp/linux/commits/Kalyazin- 
>> Nikita/KVM-guest_memfd-add-generic-population-via-write/20250828-233437
>> base:   a6ad54137af92535cfe32e19e5f3bc1bb7dbd383
>> patch link:    https://lore.kernel.org/r/20250828153049.3922-2- 
>> kalyazin%40amazon.com
>> patch subject: [PATCH v4 1/2] KVM: guest_memfd: add generic population 
>> via write
>> config: x86_64-randconfig-001-20250830 (https://download.01.org/0day- 
>> ci/archive/20250831/202508310252.E5uFh1hx-lkp@...el.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/20250831/202508310252.E5uFh1hx-lkp@...el.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/202508310252.E5uFh1hx- 
>> lkp@...el.com/
>>
>> All errors (new ones prefixed by >>, old ones prefixed by <<):
>>
>>>> ERROR: modpost: "filemap_remove_folio" [arch/x86/kvm/kvm.ko] undefined!
> 
> Right, that one is not exported.

Indeed.  Having a look at other .write_end implementations, it looks 
like the convention is zeroing the uncopied part instead of trying to 
remove the folio from the cache.  Will do it in the next version.

> 
> -- 
> Cheers
> 
> David / dhildenb
>