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qmi_wwan: allow max_mtu above hard_mtu to control rx_urb_size

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Commit c7159e960f ("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: c7159e960f ("usbnet: limit max_mtu based on device's hard_mtu")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/lkml/CAPh3n803k8JcBPV5qEzUB-oKzWkAs-D5CU7z=Vd_nLRCr5ZqQg@mail.gmail.com/
Reported-by: Koen Vandeputte <koen.vandeputte@citymesh.com>
Tested-by: Daniele Palmas <dnlplm@gmail.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Link: https://patch.msgid.link/20260304134338.1785002-1-lvivier@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Laurent Vivier
2026-03-04 14:43:38 +01:00
committed by Jakub Kicinski
parent 03910cdc21
commit 55f854dd5b
3 changed files with 7 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/net/usb/qmi_wwan.c
View File

@@ -928,7 +928,7 @@ err:
static const struct driver_info qmi_wwan_info = {
.description = "WWAN/QMI device",
.flags = FLAG_WWAN | FLAG_SEND_ZLP,
.flags = FLAG_WWAN | FLAG_NOMAXMTU | FLAG_SEND_ZLP,
.bind = qmi_wwan_bind,
.unbind = qmi_wwan_unbind,
.manage_power = qmi_wwan_manage_power,
@@ -937,7 +937,7 @@ static const struct driver_info qmi_wwan_info = {
static const struct driver_info qmi_wwan_info_quirk_dtr = {
.description = "WWAN/QMI device",
.flags = FLAG_WWAN | FLAG_SEND_ZLP,
.flags = FLAG_WWAN | FLAG_NOMAXMTU | FLAG_SEND_ZLP,
.bind = qmi_wwan_bind,
.unbind = qmi_wwan_unbind,
.manage_power = qmi_wwan_manage_power,

7
drivers/net/usb/usbnet.c
View File

@@ -1829,11 +1829,12 @@ usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod)
if ((dev->driver_info->flags & FLAG_NOARP) != 0)
net->flags |= IFF_NOARP;
if (net->max_mtu > (dev->hard_mtu - net->hard_header_len))
if ((dev->driver_info->flags & FLAG_NOMAXMTU) == 0 &&
net->max_mtu > (dev->hard_mtu - net->hard_header_len))
net->max_mtu = dev->hard_mtu - net->hard_header_len;
if (net->mtu > net->max_mtu)
net->mtu = net->max_mtu;
if (net->mtu > (dev->hard_mtu - net->hard_header_len))
net->mtu = dev->hard_mtu - net->hard_header_len;
} else if (!info->in || !info->out)
status = usbnet_get_endpoints(dev, udev);

1
include/linux/usb/usbnet.h
View File

@@ -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 */
/* init device ... can sleep, or cause probe() failure */
int (*bind)(struct usbnet *, struct usb_interface *);