mm: bring in additional flag for fixup_user_fault to signal unlock
During Jason's work with postcopy migration support for s390 a problem
regarding gmap faults was discovered.
The gmap code will call fixup_user_fault which will end up always in
handle_mm_fault. Till now we never cared about retries, but as the
userfaultfd code kind of relies on it. this needs some fix.
This patchset does not take care of the futex code. I will now look
closer at this.
This patch (of 2):
With the introduction of userfaultfd, kvm on s390 needs fixup_user_fault
to pass in FAULT_FLAG_ALLOW_RETRY and give feedback if during the
faulting we ever unlocked mmap_sem.
This patch brings in the logic to handle retries as well as it cleans up
the current documentation. fixup_user_fault was not having the same
semantics as filemap_fault. It never indicated if a retry happened and
so a caller wasn't able to handle that case. So we now changed the
behaviour to always retry a locked mmap_sem.
Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: "Jason J. Herne" <jjherne@linux.vnet.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Eric B Munson <emunson@akamai.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Dominik Dingel <dingel@linux.vnet.ibm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 792f246..1d6ec55 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1194,7 +1194,8 @@
extern int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, unsigned int flags);
extern int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
- unsigned long address, unsigned int fault_flags);
+ unsigned long address, unsigned int fault_flags,
+ bool *unlocked);
#else
static inline int handle_mm_fault(struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long address,
@@ -1206,7 +1207,7 @@
}
static inline int fixup_user_fault(struct task_struct *tsk,
struct mm_struct *mm, unsigned long address,
- unsigned int fault_flags)
+ unsigned int fault_flags, bool *unlocked)
{
/* should never happen if there's no MMU */
BUG();