[PATCH] hugetlbfs: don't delete error page from pagecache

James Houghton
2022-10-18T20:01:36Z

This change is very similar to the change that was made for shmem [1],
and it solves the same problem but for HugeTLBFS instead.

Currently, when poison is found in a HugeTLB page, the page is removed
from the page cache. That means that attempting to map or read that
hugepage in the future will result in a new hugepage being allocated
instead of notifying the user that the page was poisoned. As [1] states,
this is effectively memory corruption.

The fix is to leave the page in the page cache. If the user attempts to
use a poisoned HugeTLB page with a syscall, the syscall will fail with
EIO, the same error code that shmem uses. For attempts to map the page,
the thread will get a BUS_MCEERR_AR SIGBUS.

[1]: commit a76054266661 ("mm: shmem: don't truncate page if memory failure happens")

Signed-off-by: James Houghton <jthoughton@google.com>
---
fs/hugetlbfs/inode.c | 13 ++++++-------
mm/hugetlb.c | 4 ++++
mm/memory-failure.c | 5 ++++-
3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index fef5165b73a5..7f836f8f9db1 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -328,6 +328,12 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
} else {
unlock_page(page);

+ if (PageHWPoison(page)) {
+ put_page(page);
+ retval = -EIO;
+ break;
+ }
+
/*
* We have the page, copy it to user space buffer.
*/
@@ -1111,13 +1117,6 @@ static int hugetlbfs_migrate_folio(struct address_space *mapping,
static int hugetlbfs_error_remove_page(struct address_space *mapping,
struct page *page)
{
- struct inode *inode = mapping->host;
- pgoff_t index = page->index;
-
- hugetlb_delete_from_page_cache(page_folio(page));
- if (unlikely(hugetlb_unreserve_pages(inode, index, index + 1, 1)))
- hugetlb_fix_reserve_counts(inode);
-
return 0;
}

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 97896165fd3f..5120a9ccbf5b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6101,6 +6101,10 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,

ptl = huge_pte_lock(h, dst_mm, dst_pte);

+ ret = -EIO;
+ if (PageHWPoison(page))
+ goto out_release_unlock;
+
/*
* We allow to overwrite a pte marker: consider when both MISSING|WP
* registered, we firstly wr-protect a none pte which has no page cache
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 145bb561ddb3..bead6bccc7f2 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1080,6 +1080,7 @@ static int me_huge_page(struct page_state *ps, struct page *p)
int res;
struct page *hpage = compound_head(p);
struct address_space *mapping;
+ bool extra_pins = false;

if (!PageHuge(hpage))
return MF_DELAYED;
@@ -1087,6 +1088,8 @@ static int me_huge_page(struct page_state *ps, struct page *p)
mapping = page_mapping(hpage);
if (mapping) {
res = truncate_error_page(hpage, page_to_pfn(p), mapping);
+ /* The page is kept in page cache. */
+ extra_pins = true;
unlock_page(hpage);
} else {
unlock_page(hpage);
@@ -1104,7 +1107,7 @@ static int me_huge_page(struct page_state *ps, struct page *p)
}
}

- if (has_extra_refcount(ps, p, false))
+ if (has_extra_refcount(ps, p, extra_pins))
res = MF_FAILED;

return res;
--
2.38.0.413.g74048e4d9e-goog