Re: [PATCH v3 2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests

David Hildenbrand
2024-04-16T07:05:20Z

On 16.04.24 08:37, Alexander Gordeev wrote:
> On Mon, Apr 15, 2024 at 09:14:03PM +0200, David Hildenbrand wrote:
>>>> +retry:
>>>> + rc = walk_page_range_vma(vma, addr, vma->vm_end,
>>>> + &find_zeropage_ops, &addr);
>>>> + if (rc <= 0)
>>>> + continue;
>>>
>>> So in case an error is returned for the last vma, __s390_unshare_zeropage()
>>> finishes with that error. By contrast, the error for a non-last vma would
>>> be ignored?
>>
>> Right, it looks a bit off. walk_page_range_vma() shouldn't fail
>> unless find_zeropage_pte_entry() would fail -- which would also be
>> very unexpected.
>>
>> To handle it cleanly in case we would ever get a weird zeropage where we
>> don't expect it, we should probably just exit early.
>>
>> Something like the following (not compiled, addressing the comment below):
>
>> @@ -2618,7 +2618,8 @@ static int __s390_unshare_zeropages(struct mm_struct *mm)
>> struct vm_area_struct *vma;
>> VMA_ITERATOR(vmi, mm, 0);
>> unsigned long addr;
>> - int rc;
>> + vm_fault_t rc;
>> + int zero_page;
>
> I would use "fault" for mm faults (just like everywhere else handle_mm_fault() is
> called) and leave rc as is:
>
> vm_fault_t fault;
> int rc;

Sure, let me know once discussion here stopped whether you want a v4 or
can fix that up.

--
Cheers,

David / dhildenb