Commit 14ade6ba authored by Willem de Bruijn's avatar Willem de Bruijn Committed by Jakub Kicinski
Browse files

net: msg_zerocopy: elide page accounting if RLIM_INFINITY 



MSG_ZEROCOPY ensures that pinned user pages do not exceed the limit.
If no limit is set, skip this accounting as otherwise expensive
atomic_long operations are called for no reason.

This accounting is already skipped for privileged (CAP_IPC_LOCK)
users. Rely on the same mechanism: if no mmp->user is set,
mm_unaccount_pinned_pages does not decrement either.

Tested by running tools/testing/selftests/net/msg_zerocopy.sh with
an unprivileged user for the TXMODE binary:

    ip netns exec "${NS1}" sudo -u "{$USER}" "${BIN}" "-${IP}" ...

Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230214155740.3448763-1-willemdebruijn.kernel@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent c24a34f5

net/core/skbuff.c

+6 −2
Original line number Diff line number Diff line
@@ -1406,14 +1406,18 @@ EXPORT_SYMBOL_GPL(skb_morph); 


int mm_account_pinned_pages(struct mmpin *mmp, size_t size)

{

	unsigned long max_pg, num_pg, new_pg, old_pg;

	unsigned long max_pg, num_pg, new_pg, old_pg, rlim;

	struct user_struct *user;



	if (capable(CAP_IPC_LOCK) || !size)

		return 0;



	rlim = rlimit(RLIMIT_MEMLOCK);

	if (rlim == RLIM_INFINITY)

		return 0;



	num_pg = (size >> PAGE_SHIFT) + 2;	/* worst case */

	max_pg = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;

	max_pg = rlim >> PAGE_SHIFT;

	user = mmp->user ? : current_user();



	old_pg = atomic_long_read(&user->locked_vm);