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Subject: Re: [PATCH v4 00/13] mm/debug_vm_pgtable fixes
To: Andrew Morton <akpm@linux-foundation.org>,
 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
References: <20200902114222.181353-1-aneesh.kumar@linux.ibm.com>
 <20201013135858.f4a7f0c5f3b0a69a2a304cfe@linux-foundation.org>
 <034db663-a5bd-fd5e-b7f6-3ec31310e8e5@linux.ibm.com>
 <20201014133607.fbf63d060e331fcd6007b624@linux-foundation.org>
From: Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <6669114f-8522-c0cf-8b99-53f064b5b946@arm.com>
Date: Thu, 15 Oct 2020 08:29:25 +0530
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On 10/15/2020 02:06 AM, Andrew Morton wrote:
> On Wed, 14 Oct 2020 08:45:16 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> wrote:
> 
>>> Against mm-debug_vm_pgtable-avoid-none-pte-in-pte_clear_test.patch:
>>>
>>> https://lkml.kernel.org/r/87zh5wx51b.fsf@linux.ibm.com
>>
>>
>> yes this one we should get fixed. I was hoping someone familiar with 
>> Riscv pte updates rules would pitch in. IIUC we need to update 
>> RANDON_ORVALUE similar to how we updated it for s390 and ppc64.
>>
>>
>>   Alternatively we can do this
>>
>> modified   mm/debug_vm_pgtable.c
>> @@ -548,7 +548,7 @@ static void __init pte_clear_tests(struct mm_struct 
>> *mm, pte_t *ptep,
>>   	pte_t pte = pfn_pte(pfn, prot);
>>
>>   	pr_debug("Validating PTE clear\n");
>> -	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>> +//	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>>   	set_pte_at(mm, vaddr, ptep, pte);
>>   	barrier();
>>   	pte_clear(mm, vaddr, ptep);
>>
>> till we get that feedback from RiscV team?
> 
> Would it be better to do
> 
> #ifdef CONFIG_S390
> 	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
> #endif

I would suggest just dropping RANDOM_ORVALUE from pte_clear_tests()
possibly with a comment saying it needs to be fixed on RISCV before
being added back later.

	pte = __pte(pte_val(pte));

OR

Disable RANDOM_ORVALUE only for RISCV.

#ifndef CONFIG_RISCV
	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
#endif