1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * VAS Fault handling.
4 * Copyright 2019, IBM Corporation
5 */
6
7#define pr_fmt(fmt) "vas: " fmt
8
9#include <linux/kernel.h>
10#include <linux/types.h>
11#include <linux/slab.h>
12#include <linux/uaccess.h>
13#include <linux/kthread.h>
14#include <linux/sched/signal.h>
15#include <linux/mmu_context.h>
16#include <asm/icswx.h>
17
18#include "vas.h"
19
20/*
21 * The maximum FIFO size for fault window can be 8MB
22 * (VAS_RX_FIFO_SIZE_MAX). Using 4MB FIFO since each VAS
23 * instance will be having fault window.
24 * 8MB FIFO can be used if expects more faults for each VAS
25 * instance.
26 */
27#define VAS_FAULT_WIN_FIFO_SIZE	(4 << 20)
28
29static void dump_fifo(struct vas_instance *vinst, void *entry)
30{
31	unsigned long *end = vinst->fault_fifo + vinst->fault_fifo_size;
32	unsigned long *fifo = entry;
33	int i;
34
35	pr_err("Fault fifo size %d, Max crbs %d\n", vinst->fault_fifo_size,
36			vinst->fault_fifo_size / CRB_SIZE);
37
38	/* Dump 10 CRB entries or until end of FIFO */
39	pr_err("Fault FIFO Dump:\n");
40	for (i = 0; i < 10*(CRB_SIZE/8) && fifo < end; i += 4, fifo += 4) {
41		pr_err("[%.3d, %p]: 0x%.16lx 0x%.16lx 0x%.16lx 0x%.16lx\n",
42			i, fifo, *fifo, *(fifo+1), *(fifo+2), *(fifo+3));
43	}
44}
45
46/*
47 * Process valid CRBs in fault FIFO.
48 * NX process user space requests, return credit and update the status
49 * in CRB. If it encounters transalation error when accessing CRB or
50 * request buffers, raises interrupt on the CPU to handle the fault.
51 * It takes credit on fault window, updates nx_fault_stamp in CRB with
52 * the following information and pastes CRB in fault FIFO.
53 *
54 * pswid - window ID of the window on which the request is sent.
55 * fault_storage_addr - fault address
56 *
57 * It can raise a single interrupt for multiple faults. Expects OS to
58 * process all valid faults and return credit for each fault on user
59 * space and fault windows. This fault FIFO control will be done with
60 * credit mechanism. NX can continuously paste CRBs until credits are not
61 * available on fault window. Otherwise, returns with RMA_reject.
62 *
63 * Total credits available on fault window: FIFO_SIZE(4MB)/CRBS_SIZE(128)
64 *
65 */
66irqreturn_t vas_fault_thread_fn(int irq, void *data)
67{
68	struct vas_instance *vinst = data;
69	struct coprocessor_request_block *crb, *entry;
70	struct coprocessor_request_block buf;
71	struct pnv_vas_window *window;
72	unsigned long flags;
73	void *fifo;
74
75	crb = &buf;
76
77	/*
78	 * VAS can interrupt with multiple page faults. So process all
79	 * valid CRBs within fault FIFO until reaches invalid CRB.
80	 * We use CCW[0] and pswid to validate CRBs:
81	 *
82	 * CCW[0]	Reserved bit. When NX pastes CRB, CCW[0]=0
83	 *		OS sets this bit to 1 after reading CRB.
84	 * pswid	NX assigns window ID. Set pswid to -1 after
85	 *		reading CRB from fault FIFO.
86	 *
87	 * We exit this function if no valid CRBs are available to process.
88	 * So acquire fault_lock and reset fifo_in_progress to 0 before
89	 * exit.
90	 * In case kernel receives another interrupt with different page
91	 * fault, interrupt handler returns with IRQ_HANDLED if
92	 * fifo_in_progress is set. Means these new faults will be
93	 * handled by the current thread. Otherwise set fifo_in_progress
94	 * and return IRQ_WAKE_THREAD to wake up thread.
95	 */
96	while (true) {
97		spin_lock_irqsave(&vinst->fault_lock, flags);
98		/*
99		 * Advance the fault fifo pointer to next CRB.
100		 * Use CRB_SIZE rather than sizeof(*crb) since the latter is
101		 * aligned to CRB_ALIGN (256) but the CRB written to by VAS is
102		 * only CRB_SIZE in len.
103		 */
104		fifo = vinst->fault_fifo + (vinst->fault_crbs * CRB_SIZE);
105		entry = fifo;
106
107		if ((entry->stamp.nx.pswid == cpu_to_be32(FIFO_INVALID_ENTRY))
108			|| (entry->ccw & cpu_to_be32(CCW0_INVALID))) {
109			vinst->fifo_in_progress = 0;
110			spin_unlock_irqrestore(&vinst->fault_lock, flags);
111			return IRQ_HANDLED;
112		}
113
114		spin_unlock_irqrestore(&vinst->fault_lock, flags);
115		vinst->fault_crbs++;
116		if (vinst->fault_crbs == (vinst->fault_fifo_size / CRB_SIZE))
117			vinst->fault_crbs = 0;
118
119		memcpy(crb, fifo, CRB_SIZE);
120		entry->stamp.nx.pswid = cpu_to_be32(FIFO_INVALID_ENTRY);
121		entry->ccw |= cpu_to_be32(CCW0_INVALID);
122		/*
123		 * Return credit for the fault window.
124		 */
125		vas_return_credit(vinst->fault_win, false);
126
127		pr_devel("VAS[%d] fault_fifo %p, fifo %p, fault_crbs %d\n",
128				vinst->vas_id, vinst->fault_fifo, fifo,
129				vinst->fault_crbs);
130
131		vas_dump_crb(crb);
132		window = vas_pswid_to_window(vinst,
133				be32_to_cpu(crb->stamp.nx.pswid));
134
135		if (IS_ERR(window)) {
136			/*
137			 * We got an interrupt about a specific send
138			 * window but we can't find that window and we can't
139			 * even clean it up (return credit on user space
140			 * window).
141			 * But we should not get here.
142			 * TODO: Disable IRQ.
143			 */
144			dump_fifo(vinst, (void *)entry);
145			pr_err("VAS[%d] fault_fifo %p, fifo %p, pswid 0x%x, fault_crbs %d bad CRB?\n",
146				vinst->vas_id, vinst->fault_fifo, fifo,
147				be32_to_cpu(crb->stamp.nx.pswid),
148				vinst->fault_crbs);
149
150			WARN_ON_ONCE(1);
151		} else {
152			/*
153			 * NX sees faults only with user space windows.
154			 */
155			if (window->user_win)
156				vas_update_csb(crb, &window->vas_win.task_ref);
157			else
158				WARN_ON_ONCE(!window->user_win);
159
160			/*
161			 * Return credit for send window after processing
162			 * fault CRB.
163			 */
164			vas_return_credit(window, true);
165		}
166	}
167}
168
169irqreturn_t vas_fault_handler(int irq, void *dev_id)
170{
171	struct vas_instance *vinst = dev_id;
172	irqreturn_t ret = IRQ_WAKE_THREAD;
173	unsigned long flags;
174
175	/*
176	 * NX can generate an interrupt for multiple faults. So the
177	 * fault handler thread process all CRBs until finds invalid
178	 * entry. In case if NX sees continuous faults, it is possible
179	 * that the thread function entered with the first interrupt
180	 * can execute and process all valid CRBs.
181	 * So wake up thread only if the fault thread is not in progress.
182	 */
183	spin_lock_irqsave(&vinst->fault_lock, flags);
184
185	if (vinst->fifo_in_progress)
186		ret = IRQ_HANDLED;
187	else
188		vinst->fifo_in_progress = 1;
189
190	spin_unlock_irqrestore(&vinst->fault_lock, flags);
191
192	return ret;
193}
194
195/*
196 * Fault window is opened per VAS instance. NX pastes fault CRB in fault
197 * FIFO upon page faults.
198 */
199int vas_setup_fault_window(struct vas_instance *vinst)
200{
201	struct vas_rx_win_attr attr;
202	struct vas_window *win;
203
204	vinst->fault_fifo_size = VAS_FAULT_WIN_FIFO_SIZE;
205	vinst->fault_fifo = kzalloc(vinst->fault_fifo_size, GFP_KERNEL);
206	if (!vinst->fault_fifo) {
207		pr_err("Unable to alloc %d bytes for fault_fifo\n",
208				vinst->fault_fifo_size);
209		return -ENOMEM;
210	}
211
212	/*
213	 * Invalidate all CRB entries. NX pastes valid entry for each fault.
214	 */
215	memset(vinst->fault_fifo, FIFO_INVALID_ENTRY, vinst->fault_fifo_size);
216	vas_init_rx_win_attr(&attr, VAS_COP_TYPE_FAULT);
217
218	attr.rx_fifo_size = vinst->fault_fifo_size;
219	attr.rx_fifo = __pa(vinst->fault_fifo);
220
221	/*
222	 * Max creds is based on number of CRBs can fit in the FIFO.
223	 * (fault_fifo_size/CRB_SIZE). If 8MB FIFO is used, max creds
224	 * will be 0xffff since the receive creds field is 16bits wide.
225	 */
226	attr.wcreds_max = vinst->fault_fifo_size / CRB_SIZE;
227	attr.lnotify_lpid = 0;
228	attr.lnotify_pid = mfspr(SPRN_PID);
229	attr.lnotify_tid = mfspr(SPRN_PID);
230
231	win = vas_rx_win_open(vinst->vas_id, VAS_COP_TYPE_FAULT, &attr);
232	if (IS_ERR(win)) {
233		pr_err("VAS: Error %ld opening FaultWin\n", PTR_ERR(win));
234		kfree(vinst->fault_fifo);
235		return PTR_ERR(win);
236	}
237
238	vinst->fault_win = container_of(win, struct pnv_vas_window, vas_win);
239
240	pr_devel("VAS: Created FaultWin %d, LPID/PID/TID [%d/%d/%d]\n",
241			vinst->fault_win->vas_win.winid, attr.lnotify_lpid,
242			attr.lnotify_pid, attr.lnotify_tid);
243
244	return 0;
245}
246