Re: [RFC/PATCH v2 05/22] s390/mm: hugetlb pages within a gmap can not be freed

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On 24.01.2018 14:45, David Hildenbrand wrote:
> On 13.12.2017 13:53, Janosch Frank wrote:
>> From: Dominik Dingel <dingel@xxxxxxxxxxxxxxxxxx>
>>
>> Guests backed by huge pages could theoretically free unused pages via
>> the diagnose 10 instruction. We currently don't allow that, so we
>> don't have to refault it once it's needed again.
>>
>> Signed-off-by: Dominik Dingel <dingel@xxxxxxxxxxxxxxxxxx>
>> Reviewed-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
>> ---
>>  arch/s390/mm/gmap.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
>> index aceaeb5..056acfc 100644
>> --- a/arch/s390/mm/gmap.c
>> +++ b/arch/s390/mm/gmap.c
>> @@ -695,6 +695,9 @@ void gmap_discard(struct gmap *gmap, unsigned long from, unsigned long to)
>>  		vmaddr |= gaddr & ~PMD_MASK;
>>  		/* Find vma in the parent mm */
>>  		vma = find_vma(gmap->mm, vmaddr);
>> +		/* We do not discard pages that are backed by hugetlbfs */
>> +		if (vma && is_vm_hugetlb_page(vma))
>> +			continue;
>>  		size = min(to - gaddr, PMD_SIZE - (gaddr & ~PMD_MASK));
>>  		zap_page_range(vma, vmaddr, size);
>>  	}
>>
> 
> This check does not care about split huge pages, correct? (because we're
> checking the VMA?)
> 

Correct

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