[PATCH 3/7] cxl/mbox: Add sanitation handling machinery

[Davidlohr Bueso <dave@stgolabs.net>]

Sanitation is by definition a device-monopolizing operation, and thus
the timeslicing rules for other background commands do not apply.
As such handle this special case asynchronously and return immediately.
Subsequent changes will allow completion to be pollable from userspace
via a sysfs file interface.

For devices that don't support interrupts for notifying background
command completion, self-poll with the caveat that the poller can
be out of sync with the ready hardware, and therefore care must be
taken to not allow any new commands to go through until the poller
sees the hw completion. The poller takes the mbox_mutex to stabilize
the flagging, minimizing any runtime overhead in the send path to
check for 'sanitize_tmo' for uncommon poll scenarios. This flag
also serves for sanitation (the only user of async polling) to know
when to queue work or simply rely on irqs.

The irq case is much simpler as hardware will serialize/error
appropriately.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
---
 drivers/cxl/cxlmem.h | 16 +++++++++
 drivers/cxl/pci.c    | 79 ++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 93 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
index 8c3302fc7738..17e3ab3c641a 100644
--- a/drivers/cxl/cxlmem.h
+++ b/drivers/cxl/cxlmem.h
@@ -220,6 +220,18 @@ struct cxl_event_state {
 	struct mutex log_lock;
 };
 
+/**
+ * struct cxl_security_state - Device security state
+ *
+ * @sanitize_dwork: self-polling work item for sanitation
+ * @sanitize_tmo: self-polling timeout
+ */
+struct cxl_security_state {
+	/* below only used if device mbox irqs are not supported */
+	struct delayed_work sanitize_dwork;
+	int sanitize_tmo;
+};
+
 /**
  * struct cxl_dev_state - The driver device state
  *
@@ -256,6 +268,7 @@ struct cxl_event_state {
  * @serial: PCIe Device Serial Number
  * @doe_mbs: PCI DOE mailbox array
  * @event: event log driver state
+ * @sec: device security state
  * @mbox_send: @dev specific transport for transmitting mailbox commands
  *
  * See section 8.2.9.5.2 Capacity Configuration and Label Storage for
@@ -296,6 +309,8 @@ struct cxl_dev_state {
 
 	struct cxl_event_state event;
 
+	struct cxl_security_state sec;
+
 	int (*mbox_send)(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *cmd);
 };
 
@@ -327,6 +342,7 @@ enum cxl_opcode {
 	CXL_MBOX_OP_GET_SCAN_MEDIA_CAPS	= 0x4303,
 	CXL_MBOX_OP_SCAN_MEDIA		= 0x4304,
 	CXL_MBOX_OP_GET_SCAN_MEDIA	= 0x4305,
+	CXL_MBOX_OP_SANITIZE		= 0x4400,
 	CXL_MBOX_OP_GET_SECURITY_STATE	= 0x4500,
 	CXL_MBOX_OP_SET_PASSPHRASE	= 0x4501,
 	CXL_MBOX_OP_DISABLE_PASSPHRASE	= 0x4502,
diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index aa1bb74a52a1..bdee5273af5a 100644
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -97,6 +97,8 @@ static bool cxl_mbox_background_complete(struct cxl_dev_state *cxlds)
 static irqreturn_t cxl_pci_mbox_irq(int irq, void *id)
 {
 	struct cxl_dev_state *cxlds = id;
+	u64 reg;
+	u16 opcode;
 
 	/* spurious or raced with hw? */
 	if (!cxl_mbox_background_complete(cxlds)) {
@@ -107,12 +109,47 @@ static irqreturn_t cxl_pci_mbox_irq(int irq, void *id)
 		goto done;
 	}
 
-	/* short-circuit the wait in __cxl_pci_mbox_send_cmd() */
-	wake_up(&mbox_wait);
+	reg = readq(cxlds->regs.mbox + CXLDEV_MBOX_BG_CMD_STATUS_OFFSET);
+	opcode = FIELD_GET(CXLDEV_MBOX_BG_CMD_COMMAND_OPCODE_MASK, reg);
+
+	if (opcode == CXL_MBOX_OP_SANITIZE) {
+		dev_dbg(cxlds->dev, "Sanitation operation ended\n");
+	} else {
+		/* short-circuit the wait in __cxl_pci_mbox_send_cmd() */
+		wake_up(&mbox_wait);
+	}
 done:
 	return IRQ_HANDLED;
 }
 
+/*
+ * Sanitation operation polling mode.
+ */
+static void cxl_mbox_sanitize_work(struct work_struct *work)
+{
+	struct cxl_dev_state *cxlds;
+
+	cxlds = container_of(work, struct cxl_dev_state,
+			     sec.sanitize_dwork.work);
+
+	WARN_ON(cxlds->sec.sanitize_tmo == -1);
+
+	mutex_lock(&cxlds->mbox_mutex);
+	if (cxl_mbox_background_complete(cxlds)) {
+		cxlds->sec.sanitize_tmo = 0;
+		put_device(cxlds->dev);
+
+		dev_dbg(cxlds->dev, "Sanitation operation ended\n");
+	} else {
+		int tmo = cxlds->sec.sanitize_tmo + 10;
+
+		cxlds->sec.sanitize_tmo = min(15 * 60, tmo);
+		queue_delayed_work(system_wq,
+				   &cxlds->sec.sanitize_dwork, tmo * HZ);
+	}
+	mutex_unlock(&cxlds->mbox_mutex);
+}
+
 /**
  * __cxl_pci_mbox_send_cmd() - Execute a mailbox command
  * @cxlds: The device state to communicate with.
@@ -173,6 +210,16 @@ static int __cxl_pci_mbox_send_cmd(struct cxl_dev_state *cxlds,
 		return -EBUSY;
 	}
 
+	/*
+	 * With sanitize polling, hardware might be done and the poller still
+	 * not be in sync. Ensure no new command comes in until so. Keep the
+	 * hardware semantics and only allow device health status.
+	 */
+	if (unlikely(cxlds->sec.sanitize_tmo > 0)) {
+		if (mbox_cmd->opcode != CXL_MBOX_OP_GET_HEALTH_INFO)
+			return -EBUSY;
+	}
+
 	cmd_reg = FIELD_PREP(CXLDEV_MBOX_CMD_COMMAND_OPCODE_MASK,
 			     mbox_cmd->opcode);
 	if (mbox_cmd->size_in) {
@@ -223,6 +270,27 @@ static int __cxl_pci_mbox_send_cmd(struct cxl_dev_state *cxlds,
 		u64 bg_status_reg;
 		int i;
 
+		/*
+		 * Sanitation is a special case which monopolizes the device
+		 * in an uninterruptible state and thus cannot be timesliced.
+		 * Return immediately instead and allow userspace to poll(2)
+		 * for completion.
+		 */
+		if (mbox_cmd->opcode == CXL_MBOX_OP_SANITIZE) {
+			if (cxlds->sec.sanitize_tmo != -1) {
+				/* give first timeout a second */
+				cxlds->sec.sanitize_tmo = 1;
+				/* hold the device throughout */
+				get_device(cxlds->dev);
+				queue_delayed_work(system_wq,
+						   &cxlds->sec.sanitize_dwork,
+						   cxlds->sec.sanitize_tmo * HZ);
+			}
+
+			dev_dbg(dev, "Sanitation operation started\n");
+			return 0;
+		}
+
 		dev_dbg(dev, "Mailbox background operation (0x%04x) started\n",
 			mbox_cmd->opcode);
 
@@ -366,6 +434,9 @@ static int cxl_pci_setup_mailbox(struct cxl_dev_state *cxlds)
 		if (rc)
 			goto mbox_poll;
 
+		/* flag that irqs are enabled */
+		cxlds->sec.sanitize_tmo = -1;
+
 		writel(CXLDEV_MBOX_CTRL_BG_CMD_IRQ,
 		       cxlds->regs.mbox + CXLDEV_MBOX_CTRL_OFFSET);
 
@@ -373,7 +444,11 @@ static int cxl_pci_setup_mailbox(struct cxl_dev_state *cxlds)
 	}
 
 mbox_poll:
+	INIT_DELAYED_WORK(&cxlds->sec.sanitize_dwork,
+			  cxl_mbox_sanitize_work);
+	cxlds->sec.sanitize_tmo = 0;
 	dev_dbg(cxlds->dev, "Mailbox interrupts are unsupported");
+
 	return 0;
 }
 
-- 
2.40.0