@@ -1708,6 +1708,8 @@ extern int access_remote_vm(struct mm_struct *mm, unsigned long addr,
void *buf, int len, unsigned int gup_flags);
extern int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
unsigned long addr, void *buf, int len, unsigned int gup_flags);
+extern int access_remote_vm_locked(struct mm_struct *mm, unsigned long addr,
+ void *buf, int len, unsigned int gup_flags);
long get_user_pages_remote(struct mm_struct *mm,
unsigned long start, unsigned long nr_pages,
@@ -4726,17 +4726,17 @@ EXPORT_SYMBOL_GPL(generic_access_phys);
/*
* Access another process' address space as given in mm. If non-NULL, use the
* given task for page fault accounting.
+ * This variant assumes that the mmap_lock is already held by the caller, so
+ * doesn't take the mmap_lock.
*/
-int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
- unsigned long addr, void *buf, int len, unsigned int gup_flags)
+int __access_remote_vm_locked(struct task_struct *tsk, struct mm_struct *mm,
+ unsigned long addr, void *buf, int len,
+ unsigned int gup_flags)
{
struct vm_area_struct *vma;
void *old_buf = buf;
int write = gup_flags & FOLL_WRITE;
- if (mmap_read_lock_killable(mm))
- return 0;
-
/* ignore errors, just check how much was successfully transferred */
while (len) {
int bytes, ret, offset;
@@ -4785,9 +4785,46 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
buf += bytes;
addr += bytes;
}
+ return buf - old_buf;
+}
+
+/*
+ * Access another process' address space as given in mm. If non-NULL, use the
+ * given task for page fault accounting.
+ */
+int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
+ unsigned long addr, void *buf, int len, unsigned int gup_flags)
+{
+ int ret;
+
+ if (mmap_read_lock_killable(mm))
+ return 0;
+
+ ret = __access_remote_vm_locked(tsk, mm, addr, buf, len, gup_flags);
mmap_read_unlock(mm);
- return buf - old_buf;
+ return ret;
+}
+
+/**
+ * access_remote_vm_locked - access another process' address space, without
+ * taking the mmap_lock. This allows nested calls from callers that already have
+ * taken the lock.
+ *
+ * @mm: the mm_struct of the target address space
+ * @addr: start address to access
+ * @buf: source or destination buffer
+ * @len: number of bytes to transfer
+ * @gup_flags: flags modifying lookup behaviour
+ *
+ * The caller must hold a reference on @mm, as well as hold the mmap_lock
+ *
+ * Return: number of bytes copied from source to destination.
+ */
+int access_remote_vm_locked(struct mm_struct *mm, unsigned long addr, void *buf,
+ int len, unsigned int gup_flags)
+{
+ return __access_remote_vm_locked(NULL, mm, addr, buf, len, gup_flags);
}
/**
This allows accessing a remote vm while the mmap_lock is already held by the caller. While adding support for anonymous vma naming, show_map_vma() needs to access the remote vm to get the name of the anonymous vma. Since show_map_vma() already holds the mmap_lock, so this _locked variant was required. Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org> --- include/linux/mm.h | 2 ++ mm/memory.c | 49 ++++++++++++++++++++++++++++++++++++++++------ 2 files changed, 45 insertions(+), 6 deletions(-)