From nobody Thu Apr 9 14:59:16 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4711D21B1BF for ; Wed, 4 Mar 2026 13:43:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772631830; cv=none; b=fiOkiZMZ4nPEIMtP+YgbfbaEecqgGSfHu/pUEwbQIuy+spFoshsqvvNhYsIkDUqEfmbkWH4/cJk9985sZFGUecC3SIwnkSScQ7F6MmkZqK6PL4QPTUmO/+yIZm8nNKqfWCZ1ZAqOXl/kbdRD6kASFvpVAzWxSAaGXa7u4qmA3kA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772631830; c=relaxed/simple; bh=iEr7a1FaNizmcVWs5IiokHhBFJTdnx5UZFnO+Jh4UeE=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Vm+clqLz3W4wRgfew1B9Os9VZBlkrPblUNCMDXUnkncltKRFGm8kqeZOO93u9p4VHXAW7Q9GSX3UiC7oFWPX50HE9q+Ng4yUtR8iteHZxGAgWMFedN7U72I1tSwlInxfiDAG5LDKFDGruI8v8DJhH5FVvqbD2XhWWcJOQ/gAvrI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=g+tBDCsR; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="g+tBDCsR" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772631827; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=VT7U0xbru4/tZbnrd2xzns4lwvF3UoTO5CKY7RnOgO4=; b=g+tBDCsRG5lR/AA6x3NMbTRsqtxI+X04LwylZKEnh5Q+bNTr8zP5BtV2kwCRXRQmhEDdYB CcDpLHbUNCE0TwWub+o/EonX0H9q/i8xwTNTSvEkIQNLBKi80ox5oXhQZsqevEter2E3R6 Jz4rbQ7XjxOFm/wlghe39e5tK4shH+U= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-483-w5wiFDbfP3qdJA6QRW7PXA-1; Wed, 04 Mar 2026 08:43:44 -0500 X-MC-Unique: w5wiFDbfP3qdJA6QRW7PXA-1 X-Mimecast-MFC-AGG-ID: w5wiFDbfP3qdJA6QRW7PXA_1772631823 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 31C4B1956046; Wed, 4 Mar 2026 13:43:43 +0000 (UTC) Received: from lenovo-t14s.redhat.com (unknown [10.44.32.107]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 54734195608E; Wed, 4 Mar 2026 13:43:40 +0000 (UTC) From: Laurent Vivier To: Jakub Kicinski Cc: Koen Vandeputte , Daniele Palmas , linux-kernel@vger.kernel.org, Stefano Brivio , linux-usb@vger.kernel.org, netdev@vger.kernel.org, Laurent Vivier , stable@vger.kernel.org Subject: [PATCH v2] qmi_wwan: allow max_mtu above hard_mtu to control rx_urb_size Date: Wed, 4 Mar 2026 14:43:38 +0100 Message-ID: <20260304134338.1785002-1-lvivier@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Content-Type: text/plain; charset="utf-8" Commit c7159e960f14 ("usbnet: limit max_mtu based on device's hard_mtu") capped net->max_mtu to the device's hard_mtu in usbnet_probe(). While this correctly prevents oversized packets on standard USB network devices, it breaks the qmi_wwan driver. qmi_wwan relies on userspace (e.g. ModemManager) setting a large MTU on the wwan0 interface to configure rx_urb_size via usbnet_change_mtu(). QMI modems negotiate USB transfer sizes of 16,383 or 32,767 bytes, and the USB receive buffers must be sized accordingly. With max_mtu capped to hard_mtu (~1500 bytes), userspace can no longer raise the MTU, the receive buffers remain small, and download speeds drop from >300 Mbps to ~0.8 Mbps. Introduce a FLAG_NOMAXMTU driver flag that allows individual usbnet drivers to opt out of the max_mtu cap. Set this flag in qmi_wwan's driver_info structures to restore the previous behavior for QMI devices, while keeping the safety fix in place for all other usbnet drivers. Fixes: c7159e960f14 ("usbnet: limit max_mtu based on device's hard_mtu") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/lkml/CAPh3n803k8JcBPV5qEzUB-oKzWkAs-D5CU7z=3D= Vd_nLRCr5ZqQg@mail.gmail.com/ Reported-by: Koen Vandeputte Tested-by: Daniele Palmas Signed-off-by: Laurent Vivier --- Notes: v2: Add cc: to stable and Link: drivers/net/usb/qmi_wwan.c | 4 ++-- drivers/net/usb/usbnet.c | 7 ++++--- include/linux/usb/usbnet.h | 1 + 3 files changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c index 3a4985b582cb..05acac10cd2b 100644 --- a/drivers/net/usb/qmi_wwan.c +++ b/drivers/net/usb/qmi_wwan.c @@ -928,7 +928,7 @@ static int qmi_wwan_resume(struct usb_interface *intf) =20 static const struct driver_info qmi_wwan_info =3D { .description =3D "WWAN/QMI device", - .flags =3D FLAG_WWAN | FLAG_SEND_ZLP, + .flags =3D FLAG_WWAN | FLAG_NOMAXMTU | FLAG_SEND_ZLP, .bind =3D qmi_wwan_bind, .unbind =3D qmi_wwan_unbind, .manage_power =3D qmi_wwan_manage_power, @@ -937,7 +937,7 @@ static const struct driver_info qmi_wwan_info =3D { =20 static const struct driver_info qmi_wwan_info_quirk_dtr =3D { .description =3D "WWAN/QMI device", - .flags =3D FLAG_WWAN | FLAG_SEND_ZLP, + .flags =3D FLAG_WWAN | FLAG_NOMAXMTU | FLAG_SEND_ZLP, .bind =3D qmi_wwan_bind, .unbind =3D qmi_wwan_unbind, .manage_power =3D qmi_wwan_manage_power, diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index ed86ba87ca4e..b72ba0803392 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -1829,11 +1829,12 @@ usbnet_probe(struct usb_interface *udev, const stru= ct usb_device_id *prod) if ((dev->driver_info->flags & FLAG_NOARP) !=3D 0) net->flags |=3D IFF_NOARP; =20 - if (net->max_mtu > (dev->hard_mtu - net->hard_header_len)) + if ((dev->driver_info->flags & FLAG_NOMAXMTU) =3D=3D 0 && + net->max_mtu > (dev->hard_mtu - net->hard_header_len)) net->max_mtu =3D dev->hard_mtu - net->hard_header_len; =20 - if (net->mtu > net->max_mtu) - net->mtu =3D net->max_mtu; + if (net->mtu > (dev->hard_mtu - net->hard_header_len)) + net->mtu =3D dev->hard_mtu - net->hard_header_len; =20 } else if (!info->in || !info->out) status =3D usbnet_get_endpoints(dev, udev); diff --git a/include/linux/usb/usbnet.h b/include/linux/usb/usbnet.h index b0e84896e6ac..bbf799ccf3b3 100644 --- a/include/linux/usb/usbnet.h +++ b/include/linux/usb/usbnet.h @@ -132,6 +132,7 @@ struct driver_info { #define FLAG_MULTI_PACKET 0x2000 #define FLAG_RX_ASSEMBLE 0x4000 /* rx packets may span >1 frames */ #define FLAG_NOARP 0x8000 /* device can't do ARP */ +#define FLAG_NOMAXMTU 0x10000 /* allow max_mtu above hard_mtu */ =20 /* init device ... can sleep, or cause probe() failure */ int (*bind)(struct usbnet *, struct usb_interface *); --=20 2.53.0