Messages in this thread | | | Date | Thu, 23 Mar 2023 11:44:48 +0800 | From | "zhangpeng (AS)" <> | Subject | Re: [PATCH v2 0/3] userfaultfd: convert userfaultfd functions to use folios |
| |
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.
| |