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scm: optimize put_cmsg()

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Calling two copy_to_user() for very small regions has very high overhead.

Switch to inlined unsafe_put_user() to save one stac/clac sequence,
and avoid copy_to_user().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2021-04-15 10:37:53 -07:00 committed by David S. Miller
parent b6faf160d0
commit 38ebcf5096
1 changed files with 14 additions and 7 deletions
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21
net/core/scm.c
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@ -228,14 +228,16 @@ int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
if (msg->msg_control_is_user) {
struct cmsghdr __user *cm = msg->msg_control_user;
struct cmsghdr cmhdr;
cmhdr.cmsg_level = level;
cmhdr.cmsg_type = type;
cmhdr.cmsg_len = cmlen;
if (copy_to_user(cm, &cmhdr, sizeof cmhdr) ||
copy_to_user(CMSG_USER_DATA(cm), data, cmlen - sizeof(*cm)))
return -EFAULT;
if (!user_write_access_begin(cm, cmlen))
goto efault;
unsafe_put_user(len, &cm->cmsg_len, efault_end);
unsafe_put_user(level, &cm->cmsg_level, efault_end);
unsafe_put_user(type, &cm->cmsg_type, efault_end);
unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
cmlen - sizeof(*cm), efault_end);
user_write_access_end();
} else {
struct cmsghdr *cm = msg->msg_control;
@ -249,6 +251,11 @@ int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
msg->msg_control += cmlen;
msg->msg_controllen -= cmlen;
return 0;
efault_end:
user_write_access_end();
efault:
return -EFAULT;
}
EXPORT_SYMBOL(put_cmsg);