mm/hugetlb.c: __get_user_pages ignores certain follow_hugetlb_page errors

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")
Link: http://lkml.kernel.org/r/1500406795-58462-1-git-send-email-daniel.m.jordan@oracle.com
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Acked-by: Punit Agrawal <punit.agrawal@arm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
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: zhong jiang <zhongjiang@huawei.com>
Cc: <stable@vger.kernel.org>	[4.12.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index bc48ee783dd9..a1a0ac0ad6f6 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4078,6 +4078,7 @@ 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;
@@ -4154,11 +4155,7 @@ 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;
                         }
@@ -4213,7 +4210,7 @@ same_page:
          */
         *position = vaddr;
 
-        return i ? i : -EFAULT;
+        return i ? i : err;
 }
 
 #ifndef __HAVE_ARCH_FLUSH_HUGETLB_TLB_RANGE