powerpc/vas: Setup fault window per VAS instance

Setup fault window for each VAS instance. When NX gets a fault on
request buffer, pastes fault CRB in the corresponding fault FIFO and
then raises an interrupt to the OS. The kernel handles this fault
and process faults CRB from this FIFO.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1587016846.2275.1053.camel@hbabu-laptop

1 files changed, 77 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/powernv/vas-fault.c b/arch/powerpc/platforms/powernv/vas-fault.c
new file mode 100644
index 000000000000..404499875525
--- /dev/null
+++ b/arch/powerpc/platforms/powernv/vas-fault.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * VAS Fault handling.
+ * Copyright 2019, IBM Corporation
+ */
+
+#define pr_fmt(fmt) "vas: " fmt
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/kthread.h>
+#include <asm/icswx.h>
+
+#include "vas.h"
+
+/*
+ * The maximum FIFO size for fault window can be 8MB
+ * (VAS_RX_FIFO_SIZE_MAX). Using 4MB FIFO since each VAS
+ * instance will be having fault window.
+ * 8MB FIFO can be used if expects more faults for each VAS
+ * instance.
+ */
+#define VAS_FAULT_WIN_FIFO_SIZE	(4 << 20)
+
+/*
+ * Fault window is opened per VAS instance. NX pastes fault CRB in fault
+ * FIFO upon page faults.
+ */
+int vas_setup_fault_window(struct vas_instance *vinst)
+{
+	struct vas_rx_win_attr attr;
+
+	vinst->fault_fifo_size = VAS_FAULT_WIN_FIFO_SIZE;
+	vinst->fault_fifo = kzalloc(vinst->fault_fifo_size, GFP_KERNEL);
+	if (!vinst->fault_fifo) {
+		pr_err("Unable to alloc %d bytes for fault_fifo\n",
+				vinst->fault_fifo_size);
+		return -ENOMEM;
+	}
+
+	/*
+	 * Invalidate all CRB entries. NX pastes valid entry for each fault.
+	 */
+	memset(vinst->fault_fifo, FIFO_INVALID_ENTRY, vinst->fault_fifo_size);
+	vas_init_rx_win_attr(&attr, VAS_COP_TYPE_FAULT);
+
+	attr.rx_fifo_size = vinst->fault_fifo_size;
+	attr.rx_fifo = vinst->fault_fifo;
+
+	/*
+	 * Max creds is based on number of CRBs can fit in the FIFO.
+	 * (fault_fifo_size/CRB_SIZE). If 8MB FIFO is used, max creds
+	 * will be 0xffff since the receive creds field is 16bits wide.
+	 */
+	attr.wcreds_max = vinst->fault_fifo_size / CRB_SIZE;
+	attr.lnotify_lpid = 0;
+	attr.lnotify_pid = mfspr(SPRN_PID);
+	attr.lnotify_tid = mfspr(SPRN_PID);
+
+	vinst->fault_win = vas_rx_win_open(vinst->vas_id, VAS_COP_TYPE_FAULT,
+					&attr);
+
+	if (IS_ERR(vinst->fault_win)) {
+		pr_err("VAS: Error %ld opening FaultWin\n",
+			PTR_ERR(vinst->fault_win));
+		kfree(vinst->fault_fifo);
+		return PTR_ERR(vinst->fault_win);
+	}
+
+	pr_devel("VAS: Created FaultWin %d, LPID/PID/TID [%d/%d/%d]\n",
+			vinst->fault_win->winid, attr.lnotify_lpid,
+			attr.lnotify_pid, attr.lnotify_tid);
+
+	return 0;
+}