From 677b2a8c1f25db5b09c1ef5bf72faa39ea81d9cf Mon Sep 17 00:00:00 2001 From: Christophe Leroy Date: Fri, 14 Jan 2022 14:05:13 -0800 Subject: [PATCH] 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 Reviewed-by: Andreas Gruenbacher Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/gup.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 2c51e9748a6a..be2a41feec7d 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -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);