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Subject: Re: [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and
 FOLL_LONGTERM
To:     Ira Weiny <ira.weiny@intel.com>, Jason Gunthorpe <jgg@ziepe.ca>
CC:     Andrew Morton <akpm@linux-foundation.org>,
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References: <20191113042710.3997854-1-jhubbard@nvidia.com>
 <20191113042710.3997854-9-jhubbard@nvidia.com>
 <20191113130202.GA26068@ziepe.ca>
 <20191113191705.GE12947@iweiny-DESK2.sc.intel.com>
From:   John Hubbard <jhubbard@nvidia.com>
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Date:   Wed, 13 Nov 2019 12:19:50 -0800
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On 11/13/19 11:17 AM, Ira Weiny wrote:
...
>>> @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>>>   		flags |= FOLL_WRITE;
>>>   
>>>   	down_read(&mm->mmap_sem);
>>> -	if (mm == current->mm) {
>>> -		ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
>>> -				     vmas);
>>> -	} else {
>>> -		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
>>> -					    vmas, NULL);
>>> -		/*
>>> -		 * The lifetime of a vaddr_get_pfn() page pin is
>>> -		 * userspace-controlled. In the fs-dax case this could
>>> -		 * lead to indefinite stalls in filesystem operations.
>>> -		 * Disallow attempts to pin fs-dax pages via this
>>> -		 * interface.
>>> -		 */
>>> -		if (ret > 0 && vma_is_fsdax(vmas[0])) {
>>> -			ret = -EOPNOTSUPP;
>>> -			put_page(page[0]);
>>> -		}
>>> -	}
>>> -	up_read(&mm->mmap_sem);
>>> -
>>> +	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
>>> +				    page, NULL, NULL);
>>>   	if (ret == 1) {
>>>   		*pfn = page_to_pfn(page[0]);
>>>   		return 0;
>>
>> Mind the return with the lock held this needs some goto unwind
> 
> Ah yea...  retract my reviewed by...  :-(
> 

ooops, embarrassed that I missed that, good catch. Will repost with it fixed.



thanks,
-- 
John Hubbard
NVIDIA