From: Mike Rapoport <rppt@linux.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Mike Rapoport <rppt@linux.ibm.com>
Subject: [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults
Date: Tue, 14 May 2019 17:29:55 +0300 [thread overview]
Message-ID: <1557844195-18882-1-git-send-email-rppt@linux.ibm.com> (raw)
When get_user_pages*() is called with pages = NULL, the processing of
VM_FAULT_RETRY terminates early without actually retrying to fault-in all
the pages.
If the pages in the requested range belong to a VMA that has userfaultfd
registered, handle_userfault() returns VM_FAULT_RETRY *after* user space
has populated the page, but for the gup pre-fault case there's no actual
retry and the caller will get no pages although they are present.
This issue was uncovered when running post-copy memory restore in CRIU
after commit d9c9ce34ed5c ("x86/fpu: Fault-in user stack if
copy_fpstate_to_sigframe() fails").
After this change, the copying of FPU state to the sigframe switched from
copy_to_user() variants which caused a real page fault to get_user_pages()
with pages parameter set to NULL.
In post-copy mode of CRIU, the destination memory is managed with
userfaultfd and lack of the retry for pre-fault case in get_user_pages()
causes a crash of the restored process.
Making the pre-fault behavior of get_user_pages() the same as the "normal"
one fixes the issue.
Fixes: d9c9ce34ed5c ("x86/fpu: Fault-in user stack if copy_fpstate_to_sigframe() fails")
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
mm/gup.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 91819b8..c32ae5a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -936,10 +936,6 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
BUG_ON(ret >= nr_pages);
}
- if (!pages)
- /* If it's a prefault don't insist harder */
- return ret;
-
if (ret > 0) {
nr_pages -= ret;
pages_done += ret;
@@ -955,8 +951,12 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
pages_done = ret;
break;
}
- /* VM_FAULT_RETRY triggered, so seek to the faulting offset */
- pages += ret;
+ /*
+ * VM_FAULT_RETRY triggered, so seek to the faulting offset.
+ * For the prefault case (!pages) we only update counts.
+ */
+ if (likely(pages))
+ pages += ret;
start += ret << PAGE_SHIFT;
/*
@@ -979,7 +979,8 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
pages_done++;
if (!nr_pages)
break;
- pages++;
+ if (likely(pages))
+ pages++;
start += PAGE_SIZE;
}
if (lock_dropped && *locked) {
--
2.7.4
next prev reply other threads:[~2019-05-14 14:30 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-26 17:33 [PATCH] x86/fpu: Use fault_in_pages_writeable() for pre-faulting Sebastian Andrzej Siewior
2019-05-26 17:35 ` Sebastian Andrzej Siewior
2019-05-26 19:25 ` Hugh Dickins
2019-05-28 11:54 ` My emacs problem -- was " Pavel Machek
2019-05-29 4:18 ` Andrew Morton
2019-05-29 7:25 ` [PATCH v2] " Sebastian Andrzej Siewior
2019-05-14 14:29 ` Mike Rapoport [this message]
2019-05-16 16:25 ` [PATCH] mm/gup: continue VM_FAULT_RETRY processing event for pre-faults Andrei Vagin
2019-05-21 15:53 ` Mike Rapoport
2019-05-22 19:21 ` Andrew Morton
2019-05-22 19:43 ` Sebastian Andrzej Siewior
2019-05-24 22:22 ` Hugh Dickins
2019-05-25 8:45 ` Sebastian Andrzej Siewior
2019-05-25 18:09 ` Hugh Dickins
2019-05-26 19:36 ` Sebastian Andrzej Siewior
2019-05-26 20:17 ` Hugh Dickins
2019-05-26 17:25 ` Pavel Machek
2019-05-22 20:38 ` Mike Rapoport
2019-05-22 21:18 ` Andrew Morton
2019-06-22 17:51 ` Andrea Arcangeli
2019-06-06 17:25 ` [tip:x86/urgent] x86/fpu: Use fault_in_pages_writeable() for pre-faulting tip-bot for Hugh Dickins
2019-05-29 21:29 ` [PATCH v2] " Chris Wilson
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