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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@csgroup.eu
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Christophe Leroy 2022-01-14 14:05:13 -08:00 committed by Linus Torvalds
parent 43b9312105
commit 677b2a8c1f
1 changed files with 10 additions and 8 deletions
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18
mm/gup.c
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@ -1672,21 +1672,22 @@ size_t fault_in_writeable(char __user *uaddr, size_t size)
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 __user *uaddr, size_t size)
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);