FAILED: patch "[PATCH] ice: fix VF queue configuration with low MTU values" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 3ba4dd024d26372733d1c02e13e076c6016e3320
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026052805-scant-urologist-faac@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3ba4dd024d26372733d1c02e13e076c6016e3320 Mon Sep 17 00:00:00 2001
From: Jose Ignacio Tornos Martinez <[email protected]>
Date: Fri, 15 May 2026 11:24:09 -0700
Subject: [PATCH] ice: fix VF queue configuration with low MTU values

The ice driver's VF queue configuration validation rejects databuffer_size values below 1024 bytes, which prevents VFs from using MTU values below 871 bytes.

The iavf driver calculates databuffer_size based on the MTU using:
databuffer_size = ALIGN(MTU + LIBETH_RX_LL_LEN, 128)

where LIBETH_RX_LL_LEN = 26 (ETH_HLEN + 2*VLAN_HLEN + ETH_FCS_LEN).

For MTU values below 871:
MTU 870: 870 + 26 = 896, aligned to 128 = 896 (< 1024, rejected) MTU 871: 871 + 26 = 897, aligned to 128 = 1024 (>= 1024, accepted)

The 1024-byte minimum seems unnecessarily restrictive, because the hardware supports databuffer_size as low as 128 bytes (the alignment boundary), which should allow MTU values down to the standard minimum of 68 bytes.

I haven't found the reason why the limit was configured in the commit 9c7dd7566d18 ("ice: add validation in OP_CONFIG_VSI_QUEUES VF message"), so with no more information and since it is working, change the minimum databuffer_size validation from 1024 to 128 bytes to allow standard low MTU values while still preventing invalid configurations.

index f73d5a3e83d4..31be2f76181c 100644
@@ -840,7 +840,7 @@ int ice_vc_cfg_qs_msg(struct ice_vf *vf, u8 *msg)
 
 			if (qpi->rxq.databuffer_size != 0 &&
 			    (qpi->rxq.databuffer_size > ((16 * 1024) - 128) ||
-			     qpi->rxq.databuffer_size < 1024))
+			     qpi->rxq.databuffer_size < 128))
 				goto error_param;
 
 			ring->rx_buf_len = qpi->rxq.databuffer_size;

From: Jose Ignacio Tornos Martinez <[email protected]>

[ Upstream commit 3ba4dd024d26372733d1c02e13e076c6016e3320 ]

The ice driver's VF queue configuration validation rejects databuffer_size values below 1024 bytes, which prevents VFs from using MTU values below 871 bytes.

The iavf driver calculates databuffer_size based on the MTU using:
databuffer_size = ALIGN(MTU + LIBETH_RX_LL_LEN, 128)

where LIBETH_RX_LL_LEN = 26 (ETH_HLEN + 2*VLAN_HLEN + ETH_FCS_LEN).

For MTU values below 871:
MTU 870: 870 + 26 = 896, aligned to 128 = 896 (< 1024, rejected) MTU 871: 871 + 26 = 897, aligned to 128 = 1024 (>= 1024, accepted)

The 1024-byte minimum seems unnecessarily restrictive, because the hardware supports databuffer_size as low as 128 bytes (the alignment boundary), which should allow MTU values down to the standard minimum of 68 bytes.

I haven't found the reason why the limit was configured in the commit 9c7dd7566d18 ("ice: add validation in OP_CONFIG_VSI_QUEUES VF message"), so with no more information and since it is working, change the minimum databuffer_size validation from 1024 to 128 bytes to allow standard low MTU values while still preventing invalid configurations.

---
 drivers/net/ethernet/intel/ice/ice_virtchnl_pf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index e4e25f3ba8493..f93551ee3cb4f 100644
@@ -3585,7 +3585,7 @@ static int ice_vc_cfg_qs_msg(struct ice_vf *vf, u8 *msg)
 
 			if (qpi->rxq.databuffer_size != 0 &&
 			    (qpi->rxq.databuffer_size > ((16 * 1024) - 128) ||
-			     qpi->rxq.databuffer_size < 1024)) {
+			     qpi->rxq.databuffer_size < 128)) {
 				v_ret = VIRTCHNL_STATUS_ERR_PARAM;
 				goto error_param;
 			}

2.53.0