Messages in this thread Patch in this message | | | From | daniel.m.jordan@oracle ... | Subject | [PATCH] mm/hugetlb: __get_user_pages ignores certain follow_hugetlb_page errors | Date | Tue, 18 Jul 2017 12:39:55 -0700 |
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Commit 9a291a7c9428 ("mm/hugetlb: report -EHWPOISON not -EFAULT when FOLL_HWPOISON is specified") causes __get_user_pages to ignore certain errors from follow_hugetlb_page. After such error, __get_user_pages subsequently calls faultin_page on the same VMA and start address that follow_hugetlb_page failed on instead of returning the error immediately as it should.
In follow_hugetlb_page, when hugetlb_fault returns a value covered under VM_FAULT_ERROR, follow_hugetlb_page returns it without setting nr_pages to 0 as __get_user_pages expects in this case, which causes the following to happen in __get_user_pages: the "while (nr_pages)" check succeeds, we skip the "if (!vma..." check because we got a VMA the last time around, we find no page with follow_page_mask, and we call faultin_page, which calls hugetlb_fault for the second time.
This issue also slightly changes how __get_user_pages works. Before, it only returned error if it had made no progress (i = 0). But now, follow_hugetlb_page can clobber "i" with an error code since its new return path doesn't check for progress. So if "i" is nonzero before a failing call to follow_hugetlb_page, that indication of progress is lost and __get_user_pages can return error even if some pages were successfully pinned.
To fix this, change follow_hugetlb_page so that it updates nr_pages, allowing __get_user_pages to fail immediately and restoring the "error only if no progress" behavior to __get_user_pages.
Tested that __get_user_pages returns when expected on error from hugetlb_fault in follow_hugetlb_page.
Fixes: 9a291a7c9428 ("mm/hugetlb: report -EHWPOISON not -EFAULT when FOLL_HWPOISON is specified") Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com> Cc: James Morse <james.morse@arm.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Punit Agrawal <punit.agrawal@arm.com> Cc: zhong jiang <zhongjiang@huawei.com> --- mm/hugetlb.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 3eedb18..cc28993 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4095,6 +4095,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long vaddr = *position; unsigned long remainder = *nr_pages; struct hstate *h = hstate_vma(vma); + int err = -EFAULT; while (vaddr < vma->vm_end && remainder) { pte_t *pte; @@ -4170,11 +4171,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, } ret = hugetlb_fault(mm, vma, vaddr, fault_flags); if (ret & VM_FAULT_ERROR) { - int err = vm_fault_to_errno(ret, flags); - - if (err) - return err; - + err = vm_fault_to_errno(ret, flags); remainder = 0; break; } @@ -4229,7 +4226,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, */ *position = vaddr; - return i ? i : -EFAULT; + return i ? i : err; } #ifndef __HAVE_ARCH_FLUSH_HUGETLB_TLB_RANGE -- 1.8.3.1
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