From: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Subject: gup: avoid multiple user access locking/unlocking in fault_in_{read/write}able
fault_in_readable() and fault_in_writeable() perform __get_user() and
__put_user() in a loop, implying multiple user access locking/unlocking.
To avoid that, use user access blocks.
Link: https://lkml.kernel.org/r/720dcf79314acca1a78fae56d478cc851952149d.1637084492.git.christophe.leroy@xxxxxxxxxx
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Reviewed-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
--- a/mm/gup.c~gup-avoid-multiple-user-access-locking-unlocking-in-fault_in_read-writeable
+++ a/mm/gup.c
@@ -1672,21 +1672,22 @@ size_t fault_in_writeable(char __user *u
if (unlikely(size == 0))
return 0;
+ if (!user_write_access_begin(uaddr, size))
+ return size;
if (!PAGE_ALIGNED(uaddr)) {
- if (unlikely(__put_user(0, uaddr) != 0))
- return size;
+ unsafe_put_user(0, uaddr, out);
uaddr = (char __user *)PAGE_ALIGN((unsigned long)uaddr);
}
end = (char __user *)PAGE_ALIGN((unsigned long)start + size);
if (unlikely(end < start))
end = NULL;
while (uaddr != end) {
- if (unlikely(__put_user(0, uaddr) != 0))
- goto out;
+ unsafe_put_user(0, uaddr, out);
uaddr += PAGE_SIZE;
}
out:
+ user_write_access_end();
if (size > uaddr - start)
return size - (uaddr - start);
return 0;
@@ -1771,21 +1772,22 @@ size_t fault_in_readable(const char __us
if (unlikely(size == 0))
return 0;
+ if (!user_read_access_begin(uaddr, size))
+ return size;
if (!PAGE_ALIGNED(uaddr)) {
- if (unlikely(__get_user(c, uaddr) != 0))
- return size;
+ unsafe_get_user(c, uaddr, out);
uaddr = (const char __user *)PAGE_ALIGN((unsigned long)uaddr);
}
end = (const char __user *)PAGE_ALIGN((unsigned long)start + size);
if (unlikely(end < start))
end = NULL;
while (uaddr != end) {
- if (unlikely(__get_user(c, uaddr) != 0))
- goto out;
+ unsafe_get_user(c, uaddr, out);
uaddr += PAGE_SIZE;
}
out:
+ user_read_access_end();
(void)c;
if (size > uaddr - start)
return size - (uaddr - start);
_
