Re: [PATCH v9 06/24] mm: make pte_unmap_same compatible with SPF

[Laurent Dufour]

On 27/03/2018 23:18, David Rientjes wrote:
> On Tue, 13 Mar 2018, Laurent Dufour wrote:
> 
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 2f3e98edc94a..b6432a261e63 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1199,6 +1199,7 @@ static inline void clear_page_pfmemalloc(struct page *page)
>>  #define VM_FAULT_NEEDDSYNC  0x2000	/* ->fault did not modify page tables
>>  					 * and needs fsync() to complete (for
>>  					 * synchronous page faults in DAX) */
>> +#define VM_FAULT_PTNOTSAME 0x4000	/* Page table entries have changed */
>>  
>>  #define VM_FAULT_ERROR	(VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | \
>>  			 VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE | \
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 21b1212a0892..4bc7b0bdcb40 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -2309,21 +2309,29 @@ static bool pte_map_lock(struct vm_fault *vmf)
>>   * parts, do_swap_page must check under lock before unmapping the pte and
>>   * proceeding (but do_wp_page is only called after already making such a check;
>>   * and do_anonymous_page can safely check later on).
>> + *
>> + * pte_unmap_same() returns:
>> + *	0			if the PTE are the same
>> + *	VM_FAULT_PTNOTSAME	if the PTE are different
>> + *	VM_FAULT_RETRY		if the VMA has changed in our back during
>> + *				a speculative page fault handling.
>>   */
>> -static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
>> -				pte_t *page_table, pte_t orig_pte)
>> +static inline int pte_unmap_same(struct vm_fault *vmf)
>>  {
>> -	int same = 1;
>> +	int ret = 0;
>> +
>>  #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
>>  	if (sizeof(pte_t) > sizeof(unsigned long)) {
>> -		spinlock_t *ptl = pte_lockptr(mm, pmd);
>> -		spin_lock(ptl);
>> -		same = pte_same(*page_table, orig_pte);
>> -		spin_unlock(ptl);
>> +		if (pte_spinlock(vmf)) {
>> +			if (!pte_same(*vmf->pte, vmf->orig_pte))
>> +				ret = VM_FAULT_PTNOTSAME;
>> +			spin_unlock(vmf->ptl);
>> +		} else
>> +			ret = VM_FAULT_RETRY;
>>  	}
>>  #endif
>> -	pte_unmap(page_table);
>> -	return same;
>> +	pte_unmap(vmf->pte);
>> +	return ret;
>>  }
>>  
>>  static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
>> @@ -2913,7 +2921,8 @@ int do_swap_page(struct vm_fault *vmf)
>>  	int exclusive = 0;
>>  	int ret = 0;
> 
> Initialization is now unneeded.

I'm sorry, what "initialization" are you talking about here ?

> 
> Otherwise:
> 
> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>

Thanks,
Laurent.