Re: [PATCH v7] mm/gup: check page hwpoison status for memory recovery failures.

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Tue, Apr 06, 2021 at 10:41:23AM +0800, Aili Yao wrote:
> When we call get_user_pages() to pin user page in memory, there may be
> hwpoison page, currently, we just handle the normal case that memory
> recovery jod is correctly finished, and we will not return the hwpoison
> page to callers, but for other cases like memory recovery fails and the
> user process related pte is not correctly set invalid, we will still
> return the hwpoison page, and may touch it and lead to panic.
> 
> In gup.c, for normal page, after we call follow_page_mask(), we will
> return the related page pointer; or like another hwpoison case with pte
> invalid, it will return NULL. For NULL, we will handle it in if (!page)
> branch. In this patch, we will filter out the hwpoison page in
> follow_page_mask() and return error code for recovery failure cases.
> 
> We will check the page hwpoison status as soon as possible and avoid doing
> followed normal procedure and try not to grab related pages.
> 
> Changes since v6:
> - Fix wrong page pointer check in follow_trans_huge_pmd();
> 
> Signed-off-by: Aili Yao <yaoaili@kingsoft.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: stable@vger.kernel.org
> ---
>  mm/gup.c         | 27 +++++++++++++++++++++++----
>  mm/huge_memory.c | 11 ++++++++---
>  mm/hugetlb.c     |  8 +++++++-
>  mm/internal.h    | 13 +++++++++++++
>  4 files changed, 51 insertions(+), 8 deletions(-)

Thank you for the work.

Looking through this patch, the internal of follow_page_mask() is
very complicated so it's not easy to make this hwpoison-aware.
Now I'm getting unsure to judge that this is the best approach.
What actually I imagined might be like below (which is totally
untested, and I'm sorry about my previous misleading comments):

diff --git a/mm/gup.c b/mm/gup.c
index e40579624f10..a60a08fc7668 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1090,6 +1090,11 @@ static long __get_user_pages(struct mm_struct *mm,
 		} else if (IS_ERR(page)) {
 			ret = PTR_ERR(page);
 			goto out;
+		} else if (gup_flags & FOLL_HWPOISON && PageHWPoison(page)) {
+			if (gup_flags & FOLL_GET)
+				put_page(page);
+			ret = -EHWPOISON;
+			goto out;
 		}
 		if (pages) {
 			pages[i] = page;
@@ -1532,7 +1537,7 @@ struct page *get_dump_page(unsigned long addr)
 	if (mmap_read_lock_killable(mm))
 		return NULL;
 	ret = __get_user_pages_locked(mm, addr, 1, &page, NULL, &locked,
-				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
+				      FOLL_FORCE | FOLL_DUMP | FOLL_GET | FOLL_HWPOISON);
 	if (locked)
 		mmap_read_unlock(mm);
 	return (ret == 1) ? page : NULL;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a86a58ef132d..03c3d3225c0d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4949,6 +4949,14 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			continue;
 		}
 
+		if (flags & FOLL_HWPOISON && PageHWPoison(page)) {
+			vaddr += huge_page_size(h);
+			remainder -= pages_per_huge_page(h);
+			i += pages_per_huge_page(h);
+			spin_unlock(ptl);
+			continue;
+		}
+
 		refs = min3(pages_per_huge_page(h) - pfn_offset,
 			    (vma->vm_end - vaddr) >> PAGE_SHIFT, remainder);
 

We can surely say that this change only affects get_user_pages() callers
with FOLL_HWPOISON set, so this should pinpoint the current problem only.
A side note is that the above change on follow_hugetlb_page() has a room of
refactoring to reduce duplicated code.

Could you try to test and complete it?

Thanks,
Naoya Horiguchi