6 files changed, 68 insertions, 8 deletions
diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
index 36e213a8108d..5a50ee6f6881 100644
--- a/drivers/dma/idxd/device.c
+++ b/drivers/dma/idxd/device.c
@@ -387,6 +387,7 @@ static void idxd_wq_disable_cleanup(struct idxd_wq *wq)
 	wq->threshold = 0;
 	wq->priority = 0;
 	wq->ats_dis = 0;
+	wq->enqcmds_retries = IDXD_ENQCMDS_RETRIES;
 	clear_bit(WQ_FLAG_DEDICATED, &wq->flags);
 	clear_bit(WQ_FLAG_BLOCK_ON_FAULT, &wq->flags);
 	memset(wq->name, 0, WQ_NAME_SIZE);
diff --git a/drivers/dma/idxd/idxd.h b/drivers/dma/idxd/idxd.h
index 89e98d69115b..6b9bfdc557fe 100644
--- a/drivers/dma/idxd/idxd.h
+++ b/drivers/dma/idxd/idxd.h
@@ -52,6 +52,9 @@ enum idxd_type {
 #define IDXD_NAME_SIZE		128
 #define IDXD_PMU_EVENT_MAX	64
 
+#define IDXD_ENQCMDS_RETRIES		32
+#define IDXD_ENQCMDS_MAX_RETRIES	64
+
 struct idxd_device_driver {
 	const char *name;
 	enum idxd_dev_type *type;
@@ -173,6 +176,7 @@ struct idxd_dma_chan {
 struct idxd_wq {
 	void __iomem *portal;
 	u32 portal_offset;
+	unsigned int enqcmds_retries;
 	struct percpu_ref wq_active;
 	struct completion wq_dead;
 	struct completion wq_resurrect;
@@ -584,6 +588,7 @@ int idxd_wq_init_percpu_ref(struct idxd_wq *wq);
 int idxd_submit_desc(struct idxd_wq *wq, struct idxd_desc *desc);
 struct idxd_desc *idxd_alloc_desc(struct idxd_wq *wq, enum idxd_op_type optype);
 void idxd_free_desc(struct idxd_wq *wq, struct idxd_desc *desc);
+int idxd_enqcmds(struct idxd_wq *wq, void __iomem *portal, const void *desc);
 
 /* dmaengine */
 int idxd_register_dma_device(struct idxd_device *idxd);
diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
index 94ecd4bf0f0e..8b3afce9ea67 100644
--- a/drivers/dma/idxd/init.c
+++ b/drivers/dma/idxd/init.c
@@ -248,6 +248,7 @@ static int idxd_setup_wqs(struct idxd_device *idxd)
 		init_completion(&wq->wq_resurrect);
 		wq->max_xfer_bytes = WQ_DEFAULT_MAX_XFER;
 		wq->max_batch_size = WQ_DEFAULT_MAX_BATCH;
+		wq->enqcmds_retries = IDXD_ENQCMDS_RETRIES;
 		wq->wqcfg = kzalloc_node(idxd->wqcfg_size, GFP_KERNEL, dev_to_node(dev));
 		if (!wq->wqcfg) {
 			put_device(conf_dev);
diff --git a/drivers/dma/idxd/irq.c b/drivers/dma/idxd/irq.c
index a3bf3ea84587..0b0055a0ad2a 100644
--- a/drivers/dma/idxd/irq.c
+++ b/drivers/dma/idxd/irq.c
@@ -98,7 +98,7 @@ static void idxd_int_handle_revoke_drain(struct idxd_irq_entry *ie)
 	if (wq_dedicated(wq)) {
 		iosubmit_cmds512(portal, &desc, 1);
 	} else {
-		rc = enqcmds(portal, &desc);
+		rc = idxd_enqcmds(wq, portal, &desc);
 		/* This should not fail unless hardware failed. */
 		if (rc < 0)
 			dev_warn(dev, "Failed to submit drain desc on wq %d\n", wq->id);
diff --git a/drivers/dma/idxd/submit.c b/drivers/dma/idxd/submit.c
index 776fa81db61d..569815a84e95 100644
--- a/drivers/dma/idxd/submit.c
+++ b/drivers/dma/idxd/submit.c
@@ -123,6 +123,29 @@ static void llist_abort_desc(struct idxd_wq *wq, struct idxd_irq_entry *ie,
 		idxd_dma_complete_txd(found, IDXD_COMPLETE_ABORT, false);
 }
 
+/*
+ * ENQCMDS typically fail when the WQ is inactive or busy. On host submission, the driver
+ * has better control of number of descriptors being submitted to a shared wq by limiting
+ * the number of driver allocated descriptors to the wq size. However, when the swq is
+ * exported to a guest kernel, it may be shared with multiple guest kernels. This means
+ * the likelihood of getting busy returned on the swq when submitting goes significantly up.
+ * Having a tunable retry mechanism allows the driver to keep trying for a bit before giving
+ * up. The sysfs knob can be tuned by the system administrator.
+ */
+int idxd_enqcmds(struct idxd_wq *wq, void __iomem *portal, const void *desc)
+{
+	int rc, retries = 0;
+
+	do {
+		rc = enqcmds(portal, desc);
+		if (rc == 0)
+			break;
+		cpu_relax();
+	} while (retries++ < wq->enqcmds_retries);
+
+	return rc;
+}
+
 int idxd_submit_desc(struct idxd_wq *wq, struct idxd_desc *desc)
 {
 	struct idxd_device *idxd = wq->idxd;
@@ -166,13 +189,7 @@ int idxd_submit_desc(struct idxd_wq *wq, struct idxd_desc *desc)
 	if (wq_dedicated(wq)) {
 		iosubmit_cmds512(portal, desc->hw, 1);
 	} else {
-		/*
-		 * It's not likely that we would receive queue full rejection
-		 * since the descriptor allocation gates at wq size. If we
-		 * receive a -EAGAIN, that means something went wrong such as the
-		 * device is not accepting descriptor at all.
-		 */
-		rc = enqcmds(portal, desc->hw);
+		rc = idxd_enqcmds(wq, portal, desc->hw);
 		if (rc < 0) {
 			percpu_ref_put(&wq->wq_active);
 			/* abort operation frees the descriptor */
diff --git a/drivers/dma/idxd/sysfs.c b/drivers/dma/idxd/sysfs.c
index 90857e776273..c0fec88ff6c1 100644
--- a/drivers/dma/idxd/sysfs.c
+++ b/drivers/dma/idxd/sysfs.c
@@ -945,6 +945,41 @@ static ssize_t wq_occupancy_show(struct device *dev, struct device_attribute *at
 static struct device_attribute dev_attr_wq_occupancy =
 		__ATTR(occupancy, 0444, wq_occupancy_show, NULL);
 
+static ssize_t wq_enqcmds_retries_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	struct idxd_wq *wq = confdev_to_wq(dev);
+
+	if (wq_dedicated(wq))
+		return -EOPNOTSUPP;
+
+	return sysfs_emit(buf, "%u\n", wq->enqcmds_retries);
+}
+
+static ssize_t wq_enqcmds_retries_store(struct device *dev, struct device_attribute *attr,
+					const char *buf, size_t count)
+{
+	struct idxd_wq *wq = confdev_to_wq(dev);
+	int rc;
+	unsigned int retries;
+
+	if (wq_dedicated(wq))
+		return -EOPNOTSUPP;
+
+	rc = kstrtouint(buf, 10, &retries);
+	if (rc < 0)
+		return rc;
+
+	if (retries > IDXD_ENQCMDS_MAX_RETRIES)
+		retries = IDXD_ENQCMDS_MAX_RETRIES;
+
+	wq->enqcmds_retries = retries;
+	return count;
+}
+
+static struct device_attribute dev_attr_wq_enqcmds_retries =
+		__ATTR(enqcmds_retries, 0644, wq_enqcmds_retries_show, wq_enqcmds_retries_store);
+
 static struct attribute *idxd_wq_attributes[] = {
 	&dev_attr_wq_clients.attr,
 	&dev_attr_wq_state.attr,
@@ -961,6 +996,7 @@ static struct attribute *idxd_wq_attributes[] = {
 	&dev_attr_wq_max_batch_size.attr,
 	&dev_attr_wq_ats_disable.attr,
 	&dev_attr_wq_occupancy.attr,
+	&dev_attr_wq_enqcmds_retries.attr,
 	NULL,
 };