ena: Fix misconfiguration when requesting regular LLQ

Patch 0a33c047a443 introduced new values to
hw.ena.force_large_llq_header. The default value of 2 means no
preference, while 0 and 1 act as the previous false and true
respectively, which allowed forcefully setting regular or large LLQ.

There are 2 ways to force the driver to select regular LLQ:

1. Setting hw.ena.force_large_llq_header = 0 via sysctl.
2. Turning on ena express, which makes the recommendation by the FW to
   be regular LLQ.

When the device supports large LLQ but the driver is forced to
regular LLQ, llq_config->llq_ring_entry_size_value is never initialized
and since it is a variable allocated on the stack, it stays garbage.

Since this variable is involved in calculating max_entries_in_tx_burst,
it could cause the maximum burst size to be zero. This causes the driver
to ignore the real maximum burst size of the device, leading to driver
resets in devices that have a maximum burst size (Nitro v4 and on. see
[1] for more information).

In case the garbage value is 0, the calculation of
max_entries_in_tx_burst divides by 0 and causes kernel panic.

The patch modifies the logic to take into account all use-cases and
ensure that the relevant fields are properly initialized.

[1]: https://docs.aws.amazon.com/ec2/latest/instancetypes/ec2-nitro-instances.html

Fixes: 0a33c047a443 ("ena: Support LLQ entry size recommendation from device")
Approved by: cperciva (mentor)
Sponsored by: Amazon, Inc.
Differential Revision: https://reviews.freebsd.org/D50040

(cherry picked from commit 56c45700f2ae15755358f2da8266247613c564df)

1 files changed, 30 insertions, 11 deletions

diff --git a/sys/dev/ena/ena.c b/sys/dev/ena/ena.c
index a0d3cf28861e..f9342ad91ae2 100644
--- a/sys/dev/ena/ena.c
+++ b/sys/dev/ena/ena.c
@@ -2760,22 +2760,41 @@ static inline void
 ena_set_llq_configurations(struct ena_llq_configurations *llq_config,
     struct ena_admin_feature_llq_desc *llq, struct ena_adapter *adapter)
 {
+	bool use_large_llq;
+
 	llq_config->llq_header_location = ENA_ADMIN_INLINE_HEADER;
 	llq_config->llq_stride_ctrl = ENA_ADMIN_MULTIPLE_DESCS_PER_ENTRY;
 	llq_config->llq_num_decs_before_header =
 	    ENA_ADMIN_LLQ_NUM_DESCS_BEFORE_HEADER_2;
-	if ((llq->entry_size_ctrl_supported & ENA_ADMIN_LIST_ENTRY_SIZE_256B) != 0) {
-		if ((ena_force_large_llq_header == ENA_LLQ_HEADER_SIZE_POLICY_LARGE) ||
-		    (ena_force_large_llq_header == ENA_LLQ_HEADER_SIZE_POLICY_DEFAULT &&
-		    llq->entry_size_recommended == ENA_ADMIN_LIST_ENTRY_SIZE_256B)) {
-			llq_config->llq_ring_entry_size =
-			    ENA_ADMIN_LIST_ENTRY_SIZE_256B;
-			llq_config->llq_ring_entry_size_value = 256;
-			adapter->llq_policy = ENA_ADMIN_LIST_ENTRY_SIZE_256B;
-		}
+
+	switch (ena_force_large_llq_header)
+	{
+	case ENA_LLQ_HEADER_SIZE_POLICY_REGULAR:
+		use_large_llq = false;
+		break;
+	case ENA_LLQ_HEADER_SIZE_POLICY_LARGE:
+		use_large_llq = true;
+		break;
+	case ENA_LLQ_HEADER_SIZE_POLICY_DEFAULT:
+		use_large_llq =
+		    (llq->entry_size_recommended == ENA_ADMIN_LIST_ENTRY_SIZE_256B);
+		break;
+	default:
+		use_large_llq = false;
+		ena_log(adapter->pdev, WARN,
+		    "force_large_llq_header should have values [0-2]\n");
+		break;
+	}
+
+	if (!(llq->entry_size_ctrl_supported & ENA_ADMIN_LIST_ENTRY_SIZE_256B))
+		use_large_llq = false;
+
+	if (use_large_llq) {
+		llq_config->llq_ring_entry_size = ENA_ADMIN_LIST_ENTRY_SIZE_256B;
+		llq_config->llq_ring_entry_size_value = 256;
+		adapter->llq_policy = ENA_ADMIN_LIST_ENTRY_SIZE_256B;
 	} else {
-		llq_config->llq_ring_entry_size =
-		    ENA_ADMIN_LIST_ENTRY_SIZE_128B;
+		llq_config->llq_ring_entry_size = ENA_ADMIN_LIST_ENTRY_SIZE_128B;
 		llq_config->llq_ring_entry_size_value = 128;
 		adapter->llq_policy = ENA_ADMIN_LIST_ENTRY_SIZE_128B;
 	}