From: ZhangPeng <zhangpeng362@huawei.com>

This patch series converts several userfaultfd functions to use folios.
And this series pass the userfaultfd selftests and the LTP userfaultfd
test cases.

Change log:

v1->v2:
In patch 2:
- Rename copy_large_folio_from_user() to copy_folio_from_user().
- Delete the inner_folio.
- kmap() and kmap_atomic() are converted to kmap_local_page(). Use
  pagefault_disable() to ensure that a deadlock will not occur.
- flush_dcache_folio() is placed outside the loop.

ZhangPeng (3):
  userfaultfd: convert mcopy_atomic_pte() to use a folio
  userfaultfd: convert __mcopy_atomic_hugetlb() to use a folio
  userfaultfd: convert __mcopy_atomic() to use a folio

 include/linux/hugetlb.h  |  4 +--
 include/linux/mm.h       |  3 +-
 include/linux/shmem_fs.h |  2 +-
 mm/hugetlb.c             | 25 +++++++-------
 mm/memory.c              | 27 +++++++--------
 mm/shmem.c               | 17 +++++----
 mm/userfaultfd.c         | 74 +++++++++++++++++++---------------------
 7 files changed, 72 insertions(+), 80 deletions(-)

-- 
2.25.1

On Tue, Mar 14, 2023 at 01:13:47PM +0000, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@huawei.com>
> 
> This patch series converts several userfaultfd functions to use folios.
> And this series pass the userfaultfd selftests and the LTP userfaultfd
> test cases.

That's what you said about the earlier patchset too.  Assuming you
ran the tests, they need to be improved to fid the bug that was in the
earlier version of the patches.

On 2023/3/14 21:23, Matthew Wilcox wrote:

> On Tue, Mar 14, 2023 at 01:13:47PM +0000, Peng Zhang wrote:
>> From: ZhangPeng<zhangpeng362@huawei.com>
>>
>> This patch series converts several userfaultfd functions to use folios.
>> And this series pass the userfaultfd selftests and the LTP userfaultfd
>> test cases.
> That's what you said about the earlier patchset too.  Assuming you
> ran the tests, they need to be improved to fid the bug that was in the
> earlier version of the patches.

I did run the tests both times before sending the patches. However, the
bug in the earlier version patches[1] is a hard corner case[2] to
trigger. To trigger it, we need to call copy_large_folio_from_user()
with allow_pagefault == true, which requires hugetlb_mcopy_atomic_pte()
to return -ENOENT. This means that calling copy_large_folio_from_user()
with allow_pagefault == false failed, i.e. copy_from_user() failed.
Building a self-test that copy_from_user() fails could be difficult.

__mcopy_atomic()
	__mcopy_atomic_hugetlb()
		hugetlb_mcopy_atomic_pte()
			copy_large_folio_from_user(..., ..., false);
			// if ret_val > 0, return -ENOENT
				copy_from_user()
				// copy_from_user() needs to fail
		if (err == -ENOENT) copy_large_folio_from_user(..., ..., true);


[1] https://lore.kernel.org/all/20230314033734.481904-3-zhangpeng362@huawei.com/

> -long copy_huge_page_from_user(struct page *dst_page,
> +long copy_large_folio_from_user(struct folio *dst_folio,
>   				const void __user *usr_src,
> -				unsigned int pages_per_huge_page,
>   				bool allow_pagefault)
>   {
>   	void *page_kaddr;
>   	unsigned long i, rc = 0;
> -	unsigned long ret_val = pages_per_huge_page * PAGE_SIZE;
> +	unsigned int nr_pages = folio_nr_pages(dst_folio);
> +	unsigned long ret_val = nr_pages * PAGE_SIZE;
>   	struct page *subpage;
> +	struct folio *inner_folio;
>   
> -	for (i = 0; i < pages_per_huge_page; i++) {
> -		subpage = nth_page(dst_page, i);
> +	for (i = 0; i < nr_pages; i++) {
> +		subpage = folio_page(dst_folio, i);
> +		inner_folio = page_folio(subpage);
>   		if (allow_pagefault)
> -			page_kaddr = kmap(subpage);
> +			page_kaddr = kmap_local_folio(inner_folio, 0);
>   		else
>   			page_kaddr = kmap_atomic(subpage);
>   		rc = copy_from_user(page_kaddr,
>   				usr_src + i * PAGE_SIZE, PAGE_SIZE);
>   		if (allow_pagefault)
> -			kunmap(subpage);
> +			kunmap_local(page_kaddr);
>   		else
>   			kunmap_atomic(page_kaddr);


Thanks,
Peng.