1/*
2 * FP/SIMD context switching and fault handling
3 *
4 * Copyright (C) 2012 ARM Ltd.
5 * Author: Catalin Marinas <catalin.marinas@arm.com>
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
18 */
19
20#include <linux/cpu.h>
21#include <linux/cpu_pm.h>
22#include <linux/kernel.h>
23#include <linux/init.h>
24#include <linux/sched.h>
25#include <linux/signal.h>
26#include <linux/hardirq.h>
27
28#include <asm/fpsimd.h>
29#include <asm/cputype.h>
30
31#define FPEXC_IOF	(1 << 0)
32#define FPEXC_DZF	(1 << 1)
33#define FPEXC_OFF	(1 << 2)
34#define FPEXC_UFF	(1 << 3)
35#define FPEXC_IXF	(1 << 4)
36#define FPEXC_IDF	(1 << 7)
37
38/*
39 * In order to reduce the number of times the FPSIMD state is needlessly saved
40 * and restored, we need to keep track of two things:
41 * (a) for each task, we need to remember which CPU was the last one to have
42 *     the task's FPSIMD state loaded into its FPSIMD registers;
43 * (b) for each CPU, we need to remember which task's userland FPSIMD state has
44 *     been loaded into its FPSIMD registers most recently, or whether it has
45 *     been used to perform kernel mode NEON in the meantime.
46 *
47 * For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
48 * the id of the current CPU everytime the state is loaded onto a CPU. For (b),
49 * we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
50 * address of the userland FPSIMD state of the task that was loaded onto the CPU
51 * the most recently, or NULL if kernel mode NEON has been performed after that.
52 *
53 * With this in place, we no longer have to restore the next FPSIMD state right
54 * when switching between tasks. Instead, we can defer this check to userland
55 * resume, at which time we verify whether the CPU's fpsimd_last_state and the
56 * task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
57 * can omit the FPSIMD restore.
58 *
59 * As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
60 * indicate whether or not the userland FPSIMD state of the current task is
61 * present in the registers. The flag is set unless the FPSIMD registers of this
62 * CPU currently contain the most recent userland FPSIMD state of the current
63 * task.
64 *
65 * For a certain task, the sequence may look something like this:
66 * - the task gets scheduled in; if both the task's fpsimd_state.cpu field
67 *   contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
68 *   variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
69 *   cleared, otherwise it is set;
70 *
71 * - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
72 *   userland FPSIMD state is copied from memory to the registers, the task's
73 *   fpsimd_state.cpu field is set to the id of the current CPU, the current
74 *   CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
75 *   TIF_FOREIGN_FPSTATE flag is cleared;
76 *
77 * - the task executes an ordinary syscall; upon return to userland, the
78 *   TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is
79 *   restored;
80 *
81 * - the task executes a syscall which executes some NEON instructions; this is
82 *   preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD
83 *   register contents to memory, clears the fpsimd_last_state per-cpu variable
84 *   and sets the TIF_FOREIGN_FPSTATE flag;
85 *
86 * - the task gets preempted after kernel_neon_end() is called; as we have not
87 *   returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
88 *   whatever is in the FPSIMD registers is not saved to memory, but discarded.
89 */
90static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
91
92/*
93 * Trapped FP/ASIMD access.
94 */
95void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
96{
97	/* TODO: implement lazy context saving/restoring */
98	WARN_ON(1);
99}
100
101/*
102 * Raise a SIGFPE for the current process.
103 */
104void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
105{
106	siginfo_t info;
107	unsigned int si_code = 0;
108
109	if (esr & FPEXC_IOF)
110		si_code = FPE_FLTINV;
111	else if (esr & FPEXC_DZF)
112		si_code = FPE_FLTDIV;
113	else if (esr & FPEXC_OFF)
114		si_code = FPE_FLTOVF;
115	else if (esr & FPEXC_UFF)
116		si_code = FPE_FLTUND;
117	else if (esr & FPEXC_IXF)
118		si_code = FPE_FLTRES;
119
120	memset(&info, 0, sizeof(info));
121	info.si_signo = SIGFPE;
122	info.si_code = si_code;
123	info.si_addr = (void __user *)instruction_pointer(regs);
124
125	send_sig_info(SIGFPE, &info, current);
126}
127
128void fpsimd_thread_switch(struct task_struct *next)
129{
130	/*
131	 * Save the current FPSIMD state to memory, but only if whatever is in
132	 * the registers is in fact the most recent userland FPSIMD state of
133	 * 'current'.
134	 */
135	if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
136		fpsimd_save_state(&current->thread.fpsimd_state);
137
138	if (next->mm) {
139		/*
140		 * If we are switching to a task whose most recent userland
141		 * FPSIMD state is already in the registers of *this* cpu,
142		 * we can skip loading the state from memory. Otherwise, set
143		 * the TIF_FOREIGN_FPSTATE flag so the state will be loaded
144		 * upon the next return to userland.
145		 */
146		struct fpsimd_state *st = &next->thread.fpsimd_state;
147
148		if (__this_cpu_read(fpsimd_last_state) == st
149		    && st->cpu == smp_processor_id())
150			clear_ti_thread_flag(task_thread_info(next),
151					     TIF_FOREIGN_FPSTATE);
152		else
153			set_ti_thread_flag(task_thread_info(next),
154					   TIF_FOREIGN_FPSTATE);
155	}
156}
157
158void fpsimd_flush_thread(void)
159{
160	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
161	fpsimd_flush_task_state(current);
162	set_thread_flag(TIF_FOREIGN_FPSTATE);
163}
164
165/*
166 * Save the userland FPSIMD state of 'current' to memory, but only if the state
167 * currently held in the registers does in fact belong to 'current'
168 */
169void fpsimd_preserve_current_state(void)
170{
171	preempt_disable();
172	if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
173		fpsimd_save_state(&current->thread.fpsimd_state);
174	preempt_enable();
175}
176
177/*
178 * Load the userland FPSIMD state of 'current' from memory, but only if the
179 * FPSIMD state already held in the registers is /not/ the most recent FPSIMD
180 * state of 'current'
181 */
182void fpsimd_restore_current_state(void)
183{
184	preempt_disable();
185	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
186		struct fpsimd_state *st = &current->thread.fpsimd_state;
187
188		fpsimd_load_state(st);
189		this_cpu_write(fpsimd_last_state, st);
190		st->cpu = smp_processor_id();
191	}
192	preempt_enable();
193}
194
195/*
196 * Load an updated userland FPSIMD state for 'current' from memory and set the
197 * flag that indicates that the FPSIMD register contents are the most recent
198 * FPSIMD state of 'current'
199 */
200void fpsimd_update_current_state(struct fpsimd_state *state)
201{
202	preempt_disable();
203	fpsimd_load_state(state);
204	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
205		struct fpsimd_state *st = &current->thread.fpsimd_state;
206
207		this_cpu_write(fpsimd_last_state, st);
208		st->cpu = smp_processor_id();
209	}
210	preempt_enable();
211}
212
213/*
214 * Invalidate live CPU copies of task t's FPSIMD state
215 */
216void fpsimd_flush_task_state(struct task_struct *t)
217{
218	t->thread.fpsimd_state.cpu = NR_CPUS;
219}
220
221#ifdef CONFIG_KERNEL_MODE_NEON
222
223static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate);
224static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate);
225
226/*
227 * Kernel-side NEON support functions
228 */
229void kernel_neon_begin_partial(u32 num_regs)
230{
231	if (in_interrupt()) {
232		struct fpsimd_partial_state *s = this_cpu_ptr(
233			in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
234
235		BUG_ON(num_regs > 32);
236		fpsimd_save_partial_state(s, roundup(num_regs, 2));
237	} else {
238		/*
239		 * Save the userland FPSIMD state if we have one and if we
240		 * haven't done so already. Clear fpsimd_last_state to indicate
241		 * that there is no longer userland FPSIMD state in the
242		 * registers.
243		 */
244		preempt_disable();
245		if (current->mm &&
246		    !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
247			fpsimd_save_state(&current->thread.fpsimd_state);
248		this_cpu_write(fpsimd_last_state, NULL);
249	}
250}
251EXPORT_SYMBOL(kernel_neon_begin_partial);
252
253void kernel_neon_end(void)
254{
255	if (in_interrupt()) {
256		struct fpsimd_partial_state *s = this_cpu_ptr(
257			in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
258		fpsimd_load_partial_state(s);
259	} else {
260		preempt_enable();
261	}
262}
263EXPORT_SYMBOL(kernel_neon_end);
264
265#endif /* CONFIG_KERNEL_MODE_NEON */
266
267#ifdef CONFIG_CPU_PM
268static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
269				  unsigned long cmd, void *v)
270{
271	switch (cmd) {
272	case CPU_PM_ENTER:
273		if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
274			fpsimd_save_state(&current->thread.fpsimd_state);
275		this_cpu_write(fpsimd_last_state, NULL);
276		break;
277	case CPU_PM_EXIT:
278		if (current->mm)
279			set_thread_flag(TIF_FOREIGN_FPSTATE);
280		break;
281	case CPU_PM_ENTER_FAILED:
282	default:
283		return NOTIFY_DONE;
284	}
285	return NOTIFY_OK;
286}
287
288static struct notifier_block fpsimd_cpu_pm_notifier_block = {
289	.notifier_call = fpsimd_cpu_pm_notifier,
290};
291
292static void fpsimd_pm_init(void)
293{
294	cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block);
295}
296
297#else
298static inline void fpsimd_pm_init(void) { }
299#endif /* CONFIG_CPU_PM */
300
301#ifdef CONFIG_HOTPLUG_CPU
302static int fpsimd_cpu_hotplug_notifier(struct notifier_block *nfb,
303				       unsigned long action,
304				       void *hcpu)
305{
306	unsigned int cpu = (long)hcpu;
307
308	switch (action) {
309	case CPU_DEAD:
310	case CPU_DEAD_FROZEN:
311		per_cpu(fpsimd_last_state, cpu) = NULL;
312		break;
313	}
314	return NOTIFY_OK;
315}
316
317static struct notifier_block fpsimd_cpu_hotplug_notifier_block = {
318	.notifier_call = fpsimd_cpu_hotplug_notifier,
319};
320
321static inline void fpsimd_hotplug_init(void)
322{
323	register_cpu_notifier(&fpsimd_cpu_hotplug_notifier_block);
324}
325
326#else
327static inline void fpsimd_hotplug_init(void) { }
328#endif
329
330/*
331 * FP/SIMD support code initialisation.
332 */
333static int __init fpsimd_init(void)
334{
335	if (elf_hwcap & HWCAP_FP) {
336		fpsimd_pm_init();
337		fpsimd_hotplug_init();
338	} else {
339		pr_notice("Floating-point is not implemented\n");
340	}
341
342	if (!(elf_hwcap & HWCAP_ASIMD))
343		pr_notice("Advanced SIMD is not implemented\n");
344
345	return 0;
346}
347late_initcall(fpsimd_init);
348