linux-kernel - Re: [PATCH 06/64] mm: teach pagefault paths about range locking

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Date:   Tue, 6 Feb 2018 10:32:54 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     Davidlohr Bueso <dbueso@...e.de>, akpm@...ux-foundation.org,
        mingo@...nel.org, peterz@...radead.org, jack@...e.cz,
        mhocko@...nel.org, kirill.shutemov@...ux.intel.com,
        mawilcox@...rosoft.com, mgorman@...hsingularity.net,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/64] mm: teach pagefault paths about range locking

On Mon, 05 Feb 2018, Laurent Dufour wrote:

>> --- a/drivers/misc/sgi-gru/grufault.c
>> +++ b/drivers/misc/sgi-gru/grufault.c
>> @@ -189,7 +189,8 @@ static void get_clear_fault_map(struct gru_state *gru,
>>   */
>>  static int non_atomic_pte_lookup(struct vm_area_struct *vma,
>>  				 unsigned long vaddr, int write,
>> -				 unsigned long *paddr, int *pageshift)
>> +				 unsigned long *paddr, int *pageshift,
>> +				 struct range_lock *mmrange)
>>  {
>>  	struct page *page;
>>
>> @@ -198,7 +199,8 @@ static int non_atomic_pte_lookup(struct vm_area_struct *vma,
>>  #else
>>  	*pageshift = PAGE_SHIFT;
>>  #endif
>> -	if (get_user_pages(vaddr, 1, write ? FOLL_WRITE : 0, &page, NULL) <= 0)
>> +	if (get_user_pages(vaddr, 1, write ? FOLL_WRITE : 0,
>> +			   &page, NULL, mmrange) <= 0)
>
>There is no need to pass down the range here since underlying called
>__get_user_pages_locked() is told to not unlock the mmap_sem.
>In general get_user_pages() doesn't need a range parameter.

Yeah, you're right. At least it was a productive exercise for auditing.

Thanks,
Davidlohr