[PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[Srujana Challa]

rss_max_key_size in the virtio spec is the maximum key size supported by
the device, not a mandatory size the driver must use. Also the value 40
is a spec minimum, not a spec maximum.

The current code rejects RSS and can fail probe when the device reports a
larger rss_max_key_size than the driver buffer limit. Instead, clamp the
effective key length to min(device rss_max_key_size, NETDEV_RSS_KEY_LEN)
and keep RSS enabled.

This keeps probe working on devices that advertise larger maximum key sizes
while respecting the netdev RSS key buffer size limit.

Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
Cc: stable@vger.kernel.org
Signed-off-by: Srujana Challa <schalla@marvell.com>
---
v3:
- Moved RSS key validation checks to virtnet_validate.
- Add fixes: tag and CC -stable
v4:
- Use NETDEV_RSS_KEY_LEN instead of type_max for the maximum rss key size.
v5:
- Interpret rss_max_key_size as a maximum and clamp it to NETDEV_RSS_KEY_LEN.
- Do not disable RSS/HASH_REPORT when device rss_max_key_size exceeds NETDEV_RSS_KEY_LEN.
- Drop the separate patch that replaced the runtime check with BUILD_BUG_ON.

 drivers/net/virtio_net.c | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 022f60728721..b241c8dbb4e1 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -373,8 +373,6 @@ struct receive_queue {
 	struct xdp_buff **xsk_buffs;
 };
 
-#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
-
 /* Control VQ buffers: protected by the rtnl lock */
 struct control_buf {
 	struct virtio_net_ctrl_hdr hdr;
@@ -478,7 +476,7 @@ struct virtnet_info {
 
 	/* Must be last as it ends in a flexible-array member. */
 	TRAILING_OVERLAP(struct virtio_net_rss_config_trailer, rss_trailer, hash_key_data,
-		u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];
+		u8 rss_hash_key_data[NETDEV_RSS_KEY_LEN];
 	);
 };
 static_assert(offsetof(struct virtnet_info, rss_trailer.hash_key_data) ==
@@ -6717,6 +6715,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 	struct virtnet_info *vi;
 	u16 max_queue_pairs;
 	int mtu = 0;
+	u16 key_sz;
 
 	/* Find if host supports multiqueue/rss virtio_net device */
 	max_queue_pairs = 1;
@@ -6851,14 +6850,13 @@ static int virtnet_probe(struct virtio_device *vdev)
 	}
 
 	if (vi->has_rss || vi->has_rss_hash_report) {
-		vi->rss_key_size =
-			virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));
-		if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
-			dev_err(&vdev->dev, "rss_max_key_size=%u exceeds the limit %u.\n",
-				vi->rss_key_size, VIRTIO_NET_RSS_MAX_KEY_SIZE);
-			err = -EINVAL;
-			goto free;
-		}
+		key_sz = virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));
+
+		vi->rss_key_size = min_t(u16, key_sz, NETDEV_RSS_KEY_LEN);
+		if (key_sz > vi->rss_key_size)
+			dev_warn(&vdev->dev,
+				 "rss_max_key_size=%u exceeds driver limit %u, clamping\n",
+				 key_sz, vi->rss_key_size);
 
 		vi->rss_hash_types_supported =
 		    virtio_cread32(vdev, offsetof(struct virtio_net_config, supported_hash_types));
-- 
2.25.1

Re: [PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[Paolo Abeni]

On 3/26/26 3:23 PM, Srujana Challa wrote:
> rss_max_key_size in the virtio spec is the maximum key size supported by
> the device, not a mandatory size the driver must use. Also the value 40
> is a spec minimum, not a spec maximum.
> 
> The current code rejects RSS and can fail probe when the device reports a
> larger rss_max_key_size than the driver buffer limit. Instead, clamp the
> effective key length to min(device rss_max_key_size, NETDEV_RSS_KEY_LEN)
> and keep RSS enabled.
> 
> This keeps probe working on devices that advertise larger maximum key sizes
> while respecting the netdev RSS key buffer size limit.
> 
> Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
> Cc: stable@vger.kernel.org
> Signed-off-by: Srujana Challa <schalla@marvell.com>
> ---
> v3:
> - Moved RSS key validation checks to virtnet_validate.
> - Add fixes: tag and CC -stable
> v4:
> - Use NETDEV_RSS_KEY_LEN instead of type_max for the maximum rss key size.
> v5:
> - Interpret rss_max_key_size as a maximum and clamp it to NETDEV_RSS_KEY_LEN.
> - Do not disable RSS/HASH_REPORT when device rss_max_key_size exceeds NETDEV_RSS_KEY_LEN.
> - Drop the separate patch that replaced the runtime check with BUILD_BUG_ON.
> 
>  drivers/net/virtio_net.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 022f60728721..b241c8dbb4e1 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -373,8 +373,6 @@ struct receive_queue {
>  	struct xdp_buff **xsk_buffs;
>  };
>  
> -#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
> -
>  /* Control VQ buffers: protected by the rtnl lock */
>  struct control_buf {
>  	struct virtio_net_ctrl_hdr hdr;
> @@ -478,7 +476,7 @@ struct virtnet_info {
>  
>  	/* Must be last as it ends in a flexible-array member. */
>  	TRAILING_OVERLAP(struct virtio_net_rss_config_trailer, rss_trailer, hash_key_data,
> -		u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];
> +		u8 rss_hash_key_data[NETDEV_RSS_KEY_LEN];
>  	);
>  };
>  static_assert(offsetof(struct virtnet_info, rss_trailer.hash_key_data) ==
> @@ -6717,6 +6715,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	struct virtnet_info *vi;
>  	u16 max_queue_pairs;
>  	int mtu = 0;
> +	u16 key_sz;
>  
>  	/* Find if host supports multiqueue/rss virtio_net device */
>  	max_queue_pairs = 1;
> @@ -6851,14 +6850,13 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	}
>  
>  	if (vi->has_rss || vi->has_rss_hash_report) {
> -		vi->rss_key_size =
> -			virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));
> -		if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
> -			dev_err(&vdev->dev, "rss_max_key_size=%u exceeds the limit %u.\n",
> -				vi->rss_key_size, VIRTIO_NET_RSS_MAX_KEY_SIZE);
> -			err = -EINVAL;
> -			goto free;
> -		}
> +		key_sz = virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));
> +
> +		vi->rss_key_size = min_t(u16, key_sz, NETDEV_RSS_KEY_LEN);
> +		if (key_sz > vi->rss_key_size)
> +			dev_warn(&vdev->dev,
> +				 "rss_max_key_size=%u exceeds driver limit %u, clamping\n",
> +				 key_sz, vi->rss_key_size);

NETDEV_RSS_KEY_LEN is 256 and virtio_cread8() returns a u8. The check is
not needed, and the warning will never be printed. I think that the
BUILD_BUG_ON() you used in v4 would be better than the above chunk.

/P

RE: [EXTERNAL] Re: [PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[Srujana Challa]

> On 3/26/26 3:23 PM, Srujana Challa wrote:
> > rss_max_key_size in the virtio spec is the maximum key size supported
> > by the device, not a mandatory size the driver must use. Also the
> > value 40 is a spec minimum, not a spec maximum.
> >
> > The current code rejects RSS and can fail probe when the device
> > reports a larger rss_max_key_size than the driver buffer limit.
> > Instead, clamp the effective key length to min(device
> > rss_max_key_size, NETDEV_RSS_KEY_LEN) and keep RSS enabled.
> >
> > This keeps probe working on devices that advertise larger maximum key
> > sizes while respecting the netdev RSS key buffer size limit.
> >
> > Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Srujana Challa <schalla@marvell.com>
> > ---
> > v3:
> > - Moved RSS key validation checks to virtnet_validate.
> > - Add fixes: tag and CC -stable
> > v4:
> > - Use NETDEV_RSS_KEY_LEN instead of type_max for the maximum rss key
> size.
> > v5:
> > - Interpret rss_max_key_size as a maximum and clamp it to
> NETDEV_RSS_KEY_LEN.
> > - Do not disable RSS/HASH_REPORT when device rss_max_key_size exceeds
> NETDEV_RSS_KEY_LEN.
> > - Drop the separate patch that replaced the runtime check with
> BUILD_BUG_ON.
> >
> >  drivers/net/virtio_net.c | 20 +++++++++-----------
> >  1 file changed, 9 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index
> > 022f60728721..b241c8dbb4e1 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -373,8 +373,6 @@ struct receive_queue {
> >  	struct xdp_buff **xsk_buffs;
> >  };
> >
> > -#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
> > -
> >  /* Control VQ buffers: protected by the rtnl lock */  struct
> > control_buf {
> >  	struct virtio_net_ctrl_hdr hdr;
> > @@ -478,7 +476,7 @@ struct virtnet_info {
> >
> >  	/* Must be last as it ends in a flexible-array member. */
> >  	TRAILING_OVERLAP(struct virtio_net_rss_config_trailer, rss_trailer,
> hash_key_data,
> > -		u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];
> > +		u8 rss_hash_key_data[NETDEV_RSS_KEY_LEN];
> >  	);
> >  };
> >  static_assert(offsetof(struct virtnet_info,
> > rss_trailer.hash_key_data) == @@ -6717,6 +6715,7 @@ static int
> virtnet_probe(struct virtio_device *vdev)
> >  	struct virtnet_info *vi;
> >  	u16 max_queue_pairs;
> >  	int mtu = 0;
> > +	u16 key_sz;
> >
> >  	/* Find if host supports multiqueue/rss virtio_net device */
> >  	max_queue_pairs = 1;
> > @@ -6851,14 +6850,13 @@ static int virtnet_probe(struct virtio_device
> *vdev)
> >  	}
> >
> >  	if (vi->has_rss || vi->has_rss_hash_report) {
> > -		vi->rss_key_size =
> > -			virtio_cread8(vdev, offsetof(struct virtio_net_config,
> rss_max_key_size));
> > -		if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
> > -			dev_err(&vdev->dev, "rss_max_key_size=%u exceeds
> the limit %u.\n",
> > -				vi->rss_key_size,
> VIRTIO_NET_RSS_MAX_KEY_SIZE);
> > -			err = -EINVAL;
> > -			goto free;
> > -		}
> > +		key_sz = virtio_cread8(vdev, offsetof(struct virtio_net_config,
> > +rss_max_key_size));
> > +
> > +		vi->rss_key_size = min_t(u16, key_sz, NETDEV_RSS_KEY_LEN);
> > +		if (key_sz > vi->rss_key_size)
> > +			dev_warn(&vdev->dev,
> > +				 "rss_max_key_size=%u exceeds driver limit
> %u, clamping\n",
> > +				 key_sz, vi->rss_key_size);
> 
> NETDEV_RSS_KEY_LEN is 256 and virtio_cread8() returns a u8. The check is
> not needed, and the warning will never be printed. I think that the
> BUILD_BUG_ON() you used in v4 would be better than the above chunk.
> 
Thank you for the feedback. In net-next, NETDEV_RSS_KEY_LEN is 256. This fix is
also intended for stable kernels, where NETDEV_RSS_KEY_LEN is 52, and
I added the message to make clamping visible in that case.
I will remove the check and send the next version.  

> /P

Re: [EXTERNAL] Re: [PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[Paolo Abeni]

On 3/31/26 3:29 PM, Srujana Challa wrote:
>> On 3/26/26 3:23 PM, Srujana Challa wrote:
>>> rss_max_key_size in the virtio spec is the maximum key size supported
>>> by the device, not a mandatory size the driver must use. Also the
>>> value 40 is a spec minimum, not a spec maximum.
>>>
>>> The current code rejects RSS and can fail probe when the device
>>> reports a larger rss_max_key_size than the driver buffer limit.
>>> Instead, clamp the effective key length to min(device
>>> rss_max_key_size, NETDEV_RSS_KEY_LEN) and keep RSS enabled.
>>>
>>> This keeps probe working on devices that advertise larger maximum key
>>> sizes while respecting the netdev RSS key buffer size limit.
>>>
>>> Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Srujana Challa <schalla@marvell.com>
>>> ---
>>> v3:
>>> - Moved RSS key validation checks to virtnet_validate.
>>> - Add fixes: tag and CC -stable
>>> v4:
>>> - Use NETDEV_RSS_KEY_LEN instead of type_max for the maximum rss key
>> size.
>>> v5:
>>> - Interpret rss_max_key_size as a maximum and clamp it to
>> NETDEV_RSS_KEY_LEN.
>>> - Do not disable RSS/HASH_REPORT when device rss_max_key_size exceeds
>> NETDEV_RSS_KEY_LEN.
>>> - Drop the separate patch that replaced the runtime check with
>> BUILD_BUG_ON.
>>>
>>>  drivers/net/virtio_net.c | 20 +++++++++-----------
>>>  1 file changed, 9 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index
>>> 022f60728721..b241c8dbb4e1 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -373,8 +373,6 @@ struct receive_queue {
>>>  	struct xdp_buff **xsk_buffs;
>>>  };
>>>
>>> -#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
>>> -
>>>  /* Control VQ buffers: protected by the rtnl lock */  struct
>>> control_buf {
>>>  	struct virtio_net_ctrl_hdr hdr;
>>> @@ -478,7 +476,7 @@ struct virtnet_info {
>>>
>>>  	/* Must be last as it ends in a flexible-array member. */
>>>  	TRAILING_OVERLAP(struct virtio_net_rss_config_trailer, rss_trailer,
>> hash_key_data,
>>> -		u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];
>>> +		u8 rss_hash_key_data[NETDEV_RSS_KEY_LEN];
>>>  	);
>>>  };
>>>  static_assert(offsetof(struct virtnet_info,
>>> rss_trailer.hash_key_data) == @@ -6717,6 +6715,7 @@ static int
>> virtnet_probe(struct virtio_device *vdev)
>>>  	struct virtnet_info *vi;
>>>  	u16 max_queue_pairs;
>>>  	int mtu = 0;
>>> +	u16 key_sz;
>>>
>>>  	/* Find if host supports multiqueue/rss virtio_net device */
>>>  	max_queue_pairs = 1;
>>> @@ -6851,14 +6850,13 @@ static int virtnet_probe(struct virtio_device
>> *vdev)
>>>  	}
>>>
>>>  	if (vi->has_rss || vi->has_rss_hash_report) {
>>> -		vi->rss_key_size =
>>> -			virtio_cread8(vdev, offsetof(struct virtio_net_config,
>> rss_max_key_size));
>>> -		if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
>>> -			dev_err(&vdev->dev, "rss_max_key_size=%u exceeds
>> the limit %u.\n",
>>> -				vi->rss_key_size,
>> VIRTIO_NET_RSS_MAX_KEY_SIZE);
>>> -			err = -EINVAL;
>>> -			goto free;
>>> -		}
>>> +		key_sz = virtio_cread8(vdev, offsetof(struct virtio_net_config,
>>> +rss_max_key_size));
>>> +
>>> +		vi->rss_key_size = min_t(u16, key_sz, NETDEV_RSS_KEY_LEN);
>>> +		if (key_sz > vi->rss_key_size)
>>> +			dev_warn(&vdev->dev,
>>> +				 "rss_max_key_size=%u exceeds driver limit
>> %u, clamping\n",
>>> +				 key_sz, vi->rss_key_size);
>>
>> NETDEV_RSS_KEY_LEN is 256 and virtio_cread8() returns a u8. The check is
>> not needed, and the warning will never be printed. I think that the
>> BUILD_BUG_ON() you used in v4 would be better than the above chunk.
>>
> Thank you for the feedback. In net-next, NETDEV_RSS_KEY_LEN is 256. This fix is
> also intended for stable kernels, where NETDEV_RSS_KEY_LEN is 52, and
> I added the message to make clamping visible in that case.
> I will remove the check and send the next version.  

I'm sorry, I haven't looked at the historical context when I wrote my
previous reply.

IMHO the additional check does not make sense in the current net tree.
On the flip side stable trees will need it. I suggest:

- dropping the check for the 'net' patch
- also dropping CC: stable tag
- explicitly sending to stable the fix variant including the size check.

@Michael: WDYT?

/P

Re: [EXTERNAL] Re: [PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[Michael S. Tsirkin]

On Tue, Mar 31, 2026 at 04:39:02PM +0200, Paolo Abeni wrote:
> On 3/31/26 3:29 PM, Srujana Challa wrote:
> >> On 3/26/26 3:23 PM, Srujana Challa wrote:
> >>> rss_max_key_size in the virtio spec is the maximum key size supported
> >>> by the device, not a mandatory size the driver must use. Also the
> >>> value 40 is a spec minimum, not a spec maximum.
> >>>
> >>> The current code rejects RSS and can fail probe when the device
> >>> reports a larger rss_max_key_size than the driver buffer limit.
> >>> Instead, clamp the effective key length to min(device
> >>> rss_max_key_size, NETDEV_RSS_KEY_LEN) and keep RSS enabled.
> >>>
> >>> This keeps probe working on devices that advertise larger maximum key
> >>> sizes while respecting the netdev RSS key buffer size limit.
> >>>
> >>> Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
> >>> Cc: stable@vger.kernel.org
> >>> Signed-off-by: Srujana Challa <schalla@marvell.com>
> >>> ---
> >>> v3:
> >>> - Moved RSS key validation checks to virtnet_validate.
> >>> - Add fixes: tag and CC -stable
> >>> v4:
> >>> - Use NETDEV_RSS_KEY_LEN instead of type_max for the maximum rss key
> >> size.
> >>> v5:
> >>> - Interpret rss_max_key_size as a maximum and clamp it to
> >> NETDEV_RSS_KEY_LEN.
> >>> - Do not disable RSS/HASH_REPORT when device rss_max_key_size exceeds
> >> NETDEV_RSS_KEY_LEN.
> >>> - Drop the separate patch that replaced the runtime check with
> >> BUILD_BUG_ON.
> >>>
> >>>  drivers/net/virtio_net.c | 20 +++++++++-----------
> >>>  1 file changed, 9 insertions(+), 11 deletions(-)
> >>>
> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index
> >>> 022f60728721..b241c8dbb4e1 100644
> >>> --- a/drivers/net/virtio_net.c
> >>> +++ b/drivers/net/virtio_net.c
> >>> @@ -373,8 +373,6 @@ struct receive_queue {
> >>>  	struct xdp_buff **xsk_buffs;
> >>>  };
> >>>
> >>> -#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
> >>> -
> >>>  /* Control VQ buffers: protected by the rtnl lock */  struct
> >>> control_buf {
> >>>  	struct virtio_net_ctrl_hdr hdr;
> >>> @@ -478,7 +476,7 @@ struct virtnet_info {
> >>>
> >>>  	/* Must be last as it ends in a flexible-array member. */
> >>>  	TRAILING_OVERLAP(struct virtio_net_rss_config_trailer, rss_trailer,
> >> hash_key_data,
> >>> -		u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];
> >>> +		u8 rss_hash_key_data[NETDEV_RSS_KEY_LEN];
> >>>  	);
> >>>  };
> >>>  static_assert(offsetof(struct virtnet_info,
> >>> rss_trailer.hash_key_data) == @@ -6717,6 +6715,7 @@ static int
> >> virtnet_probe(struct virtio_device *vdev)
> >>>  	struct virtnet_info *vi;
> >>>  	u16 max_queue_pairs;
> >>>  	int mtu = 0;
> >>> +	u16 key_sz;
> >>>
> >>>  	/* Find if host supports multiqueue/rss virtio_net device */
> >>>  	max_queue_pairs = 1;
> >>> @@ -6851,14 +6850,13 @@ static int virtnet_probe(struct virtio_device
> >> *vdev)
> >>>  	}
> >>>
> >>>  	if (vi->has_rss || vi->has_rss_hash_report) {
> >>> -		vi->rss_key_size =
> >>> -			virtio_cread8(vdev, offsetof(struct virtio_net_config,
> >> rss_max_key_size));
> >>> -		if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
> >>> -			dev_err(&vdev->dev, "rss_max_key_size=%u exceeds
> >> the limit %u.\n",
> >>> -				vi->rss_key_size,
> >> VIRTIO_NET_RSS_MAX_KEY_SIZE);
> >>> -			err = -EINVAL;
> >>> -			goto free;
> >>> -		}
> >>> +		key_sz = virtio_cread8(vdev, offsetof(struct virtio_net_config,
> >>> +rss_max_key_size));
> >>> +
> >>> +		vi->rss_key_size = min_t(u16, key_sz, NETDEV_RSS_KEY_LEN);
> >>> +		if (key_sz > vi->rss_key_size)
> >>> +			dev_warn(&vdev->dev,
> >>> +				 "rss_max_key_size=%u exceeds driver limit
> >> %u, clamping\n",
> >>> +				 key_sz, vi->rss_key_size);
> >>
> >> NETDEV_RSS_KEY_LEN is 256 and virtio_cread8() returns a u8. The check is
> >> not needed, and the warning will never be printed. I think that the
> >> BUILD_BUG_ON() you used in v4 would be better than the above chunk.
> >>
> > Thank you for the feedback. In net-next, NETDEV_RSS_KEY_LEN is 256. This fix is
> > also intended for stable kernels, where NETDEV_RSS_KEY_LEN is 52, and
> > I added the message to make clamping visible in that case.
> > I will remove the check and send the next version.  
> 
> I'm sorry, I haven't looked at the historical context when I wrote my
> previous reply.
> 
> IMHO the additional check does not make sense in the current net tree.
> On the flip side stable trees will need it. I suggest:
> 
> - dropping the check for the 'net' patch
> - also dropping CC: stable tag
> - explicitly sending to stable the fix variant including the size check.
> 
> @Michael: WDYT?
> 
> /P

I was the one who suggested it, the extra check is harmless, I'm
inclined to always have it.  Less work than maintaining two patches.

-- 
MST

Re: [EXTERNAL] Re: [PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[Jakub Kicinski]

On Tue, 31 Mar 2026 10:48:41 -0400 Michael S. Tsirkin wrote:
> > > Thank you for the feedback. In net-next, NETDEV_RSS_KEY_LEN is 256. This fix is
> > > also intended for stable kernels, where NETDEV_RSS_KEY_LEN is 52, and
> > > I added the message to make clamping visible in that case.
> > > I will remove the check and send the next version.    
> > 
> > I'm sorry, I haven't looked at the historical context when I wrote my
> > previous reply.
> > 
> > IMHO the additional check does not make sense in the current net tree.
> > On the flip side stable trees will need it. I suggest:
> > 
> > - dropping the check for the 'net' patch
> > - also dropping CC: stable tag
> > - explicitly sending to stable the fix variant including the size check.
> > 
> > @Michael: WDYT?
>
> I was the one who suggested it, the extra check is harmless, I'm
> inclined to always have it.  Less work than maintaining two patches.

Give us an RB tag please and lets close this one? :)

Re: [PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[Michael S. Tsirkin]

On Thu, Mar 26, 2026 at 07:53:44PM +0530, Srujana Challa wrote:
> rss_max_key_size in the virtio spec is the maximum key size supported by
> the device, not a mandatory size the driver must use. Also the value 40
> is a spec minimum, not a spec maximum.
> 
> The current code rejects RSS and can fail probe when the device reports a
> larger rss_max_key_size than the driver buffer limit. Instead, clamp the
> effective key length to min(device rss_max_key_size, NETDEV_RSS_KEY_LEN)
> and keep RSS enabled.
> 
> This keeps probe working on devices that advertise larger maximum key sizes
> while respecting the netdev RSS key buffer size limit.
> 
> Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
> Cc: stable@vger.kernel.org
> Signed-off-by: Srujana Challa <schalla@marvell.com>


Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
> v3:
> - Moved RSS key validation checks to virtnet_validate.
> - Add fixes: tag and CC -stable
> v4:
> - Use NETDEV_RSS_KEY_LEN instead of type_max for the maximum rss key size.
> v5:
> - Interpret rss_max_key_size as a maximum and clamp it to NETDEV_RSS_KEY_LEN.
> - Do not disable RSS/HASH_REPORT when device rss_max_key_size exceeds NETDEV_RSS_KEY_LEN.
> - Drop the separate patch that replaced the runtime check with BUILD_BUG_ON.
> 
>  drivers/net/virtio_net.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 022f60728721..b241c8dbb4e1 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -373,8 +373,6 @@ struct receive_queue {
>  	struct xdp_buff **xsk_buffs;
>  };
>  
> -#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
> -
>  /* Control VQ buffers: protected by the rtnl lock */
>  struct control_buf {
>  	struct virtio_net_ctrl_hdr hdr;
> @@ -478,7 +476,7 @@ struct virtnet_info {
>  
>  	/* Must be last as it ends in a flexible-array member. */
>  	TRAILING_OVERLAP(struct virtio_net_rss_config_trailer, rss_trailer, hash_key_data,
> -		u8 rss_hash_key_data[VIRTIO_NET_RSS_MAX_KEY_SIZE];
> +		u8 rss_hash_key_data[NETDEV_RSS_KEY_LEN];
>  	);
>  };
>  static_assert(offsetof(struct virtnet_info, rss_trailer.hash_key_data) ==
> @@ -6717,6 +6715,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	struct virtnet_info *vi;
>  	u16 max_queue_pairs;
>  	int mtu = 0;
> +	u16 key_sz;
>  
>  	/* Find if host supports multiqueue/rss virtio_net device */
>  	max_queue_pairs = 1;
> @@ -6851,14 +6850,13 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	}
>  
>  	if (vi->has_rss || vi->has_rss_hash_report) {
> -		vi->rss_key_size =
> -			virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));
> -		if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
> -			dev_err(&vdev->dev, "rss_max_key_size=%u exceeds the limit %u.\n",
> -				vi->rss_key_size, VIRTIO_NET_RSS_MAX_KEY_SIZE);
> -			err = -EINVAL;
> -			goto free;
> -		}
> +		key_sz = virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));
> +
> +		vi->rss_key_size = min_t(u16, key_sz, NETDEV_RSS_KEY_LEN);
> +		if (key_sz > vi->rss_key_size)
> +			dev_warn(&vdev->dev,
> +				 "rss_max_key_size=%u exceeds driver limit %u, clamping\n",
> +				 key_sz, vi->rss_key_size);
>  
>  		vi->rss_hash_types_supported =
>  		    virtio_cread32(vdev, offsetof(struct virtio_net_config, supported_hash_types));
> -- 
> 2.25.1

Re: [EXTERNAL] Re: [PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[Michael S. Tsirkin]

On Tue, Mar 31, 2026 at 06:05:22PM -0700, Jakub Kicinski wrote:
> On Tue, 31 Mar 2026 10:48:41 -0400 Michael S. Tsirkin wrote:
> > > > Thank you for the feedback. In net-next, NETDEV_RSS_KEY_LEN is 256. This fix is
> > > > also intended for stable kernels, where NETDEV_RSS_KEY_LEN is 52, and
> > > > I added the message to make clamping visible in that case.
> > > > I will remove the check and send the next version.    
> > > 
> > > I'm sorry, I haven't looked at the historical context when I wrote my
> > > previous reply.
> > > 
> > > IMHO the additional check does not make sense in the current net tree.
> > > On the flip side stable trees will need it. I suggest:
> > > 
> > > - dropping the check for the 'net' patch
> > > - also dropping CC: stable tag
> > > - explicitly sending to stable the fix variant including the size check.
> > > 
> > > @Michael: WDYT?
> >
> > I was the one who suggested it, the extra check is harmless, I'm
> > inclined to always have it.  Less work than maintaining two patches.
> 
> Give us an RB tag please and lets close this one? :)

Oh I thought I did. Thanks.

Re: [PATCH net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 26 Mar 2026 19:53:44 +0530 you wrote:
> rss_max_key_size in the virtio spec is the maximum key size supported by
> the device, not a mandatory size the driver must use. Also the value 40
> is a spec minimum, not a spec maximum.
> 
> The current code rejects RSS and can fail probe when the device reports a
> larger rss_max_key_size than the driver buffer limit. Instead, clamp the
> effective key length to min(device rss_max_key_size, NETDEV_RSS_KEY_LEN)
> and keep RSS enabled.
> 
> [...]

Here is the summary with links:
  - [net,v5] virtio_net: clamp rss_max_key_size to NETDEV_RSS_KEY_LEN
    https://git.kernel.org/netdev/net/c/b4e5f04c58a2

You are awesome, thank you!
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