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_pm.h>
21#include <linux/kernel.h>
22#include <linux/init.h>
23#include <linux/sched.h>
24#include <linux/signal.h>
25#include <linux/hardirq.h>
26
27#include <asm/fpsimd.h>
28#include <asm/cputype.h>
29
30#define FPEXC_IOF	(1 << 0)
31#define FPEXC_DZF	(1 << 1)
32#define FPEXC_OFF	(1 << 2)
33#define FPEXC_UFF	(1 << 3)
34#define FPEXC_IXF	(1 << 4)
35#define FPEXC_IDF	(1 << 7)
36
37/*
38 * In order to reduce the number of times the FPSIMD state is needlessly saved
39 * and restored, we need to keep track of two things:
40 * (a) for each task, we need to remember which CPU was the last one to have
41 *     the task's FPSIMD state loaded into its FPSIMD registers;
42 * (b) for each CPU, we need to remember which task's userland FPSIMD state has
43 *     been loaded into its FPSIMD registers most recently, or whether it has
44 *     been used to perform kernel mode NEON in the meantime.
45 *
46 * For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
47 * the id of the current CPU everytime the state is loaded onto a CPU. For (b),
48 * we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
49 * address of the userland FPSIMD state of the task that was loaded onto the CPU
50 * the most recently, or NULL if kernel mode NEON has been performed after that.
51 *
52 * With this in place, we no longer have to restore the next FPSIMD state right
53 * when switching between tasks. Instead, we can defer this check to userland
54 * resume, at which time we verify whether the CPU's fpsimd_last_state and the
55 * task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
56 * can omit the FPSIMD restore.
57 *
58 * As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
59 * indicate whether or not the userland FPSIMD state of the current task is
60 * present in the registers. The flag is set unless the FPSIMD registers of this
61 * CPU currently contain the most recent userland FPSIMD state of the current
62 * task.
63 *
64 * For a certain task, the sequence may look something like this:
65 * - the task gets scheduled in; if both the task's fpsimd_state.cpu field
66 *   contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
67 *   variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
68 *   cleared, otherwise it is set;
69 *
70 * - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
71 *   userland FPSIMD state is copied from memory to the registers, the task's
72 *   fpsimd_state.cpu field is set to the id of the current CPU, the current
73 *   CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
74 *   TIF_FOREIGN_FPSTATE flag is cleared;
75 *
76 * - the task executes an ordinary syscall; upon return to userland, the
77 *   TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is
78 *   restored;
79 *
80 * - the task executes a syscall which executes some NEON instructions; this is
81 *   preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD
82 *   register contents to memory, clears the fpsimd_last_state per-cpu variable
83 *   and sets the TIF_FOREIGN_FPSTATE flag;
84 *
85 * - the task gets preempted after kernel_neon_end() is called; as we have not
86 *   returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
87 *   whatever is in the FPSIMD registers is not saved to memory, but discarded.
88 */
89static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
90
91/*
92 * Trapped FP/ASIMD access.
93 */
94void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
95{
96	/* TODO: implement lazy context saving/restoring */
97	WARN_ON(1);
98}
99
100/*
101 * Raise a SIGFPE for the current process.
102 */
103void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
104{
105	siginfo_t info;
106	unsigned int si_code = 0;
107
108	if (esr & FPEXC_IOF)
109		si_code = FPE_FLTINV;
110	else if (esr & FPEXC_DZF)
111		si_code = FPE_FLTDIV;
112	else if (esr & FPEXC_OFF)
113		si_code = FPE_FLTOVF;
114	else if (esr & FPEXC_UFF)
115		si_code = FPE_FLTUND;
116	else if (esr & FPEXC_IXF)
117		si_code = FPE_FLTRES;
118
119	memset(&info, 0, sizeof(info));
120	info.si_signo = SIGFPE;
121	info.si_code = si_code;
122	info.si_addr = (void __user *)instruction_pointer(regs);
123
124	send_sig_info(SIGFPE, &info, current);
125}
126
127void fpsimd_thread_switch(struct task_struct *next)
128{
129	/*
130	 * Save the current FPSIMD state to memory, but only if whatever is in
131	 * the registers is in fact the most recent userland FPSIMD state of
132	 * 'current'.
133	 */
134	if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
135		fpsimd_save_state(&current->thread.fpsimd_state);
136
137	if (next->mm) {
138		/*
139		 * If we are switching to a task whose most recent userland
140		 * FPSIMD state is already in the registers of *this* cpu,
141		 * we can skip loading the state from memory. Otherwise, set
142		 * the TIF_FOREIGN_FPSTATE flag so the state will be loaded
143		 * upon the next return to userland.
144		 */
145		struct fpsimd_state *st = &next->thread.fpsimd_state;
146
147		if (__this_cpu_read(fpsimd_last_state) == st
148		    && st->cpu == smp_processor_id())
149			clear_ti_thread_flag(task_thread_info(next),
150					     TIF_FOREIGN_FPSTATE);
151		else
152			set_ti_thread_flag(task_thread_info(next),
153					   TIF_FOREIGN_FPSTATE);
154	}
155}
156
157void fpsimd_flush_thread(void)
158{
159	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
160	fpsimd_flush_task_state(current);
161	set_thread_flag(TIF_FOREIGN_FPSTATE);
162}
163
164/*
165 * Save the userland FPSIMD state of 'current' to memory, but only if the state
166 * currently held in the registers does in fact belong to 'current'
167 */
168void fpsimd_preserve_current_state(void)
169{
170	preempt_disable();
171	if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
172		fpsimd_save_state(&current->thread.fpsimd_state);
173	preempt_enable();
174}
175
176/*
177 * Load the userland FPSIMD state of 'current' from memory, but only if the
178 * FPSIMD state already held in the registers is /not/ the most recent FPSIMD
179 * state of 'current'
180 */
181void fpsimd_restore_current_state(void)
182{
183	preempt_disable();
184	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
185		struct fpsimd_state *st = &current->thread.fpsimd_state;
186
187		fpsimd_load_state(st);
188		this_cpu_write(fpsimd_last_state, st);
189		st->cpu = smp_processor_id();
190	}
191	preempt_enable();
192}
193
194/*
195 * Load an updated userland FPSIMD state for 'current' from memory and set the
196 * flag that indicates that the FPSIMD register contents are the most recent
197 * FPSIMD state of 'current'
198 */
199void fpsimd_update_current_state(struct fpsimd_state *state)
200{
201	preempt_disable();
202	fpsimd_load_state(state);
203	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
204		struct fpsimd_state *st = &current->thread.fpsimd_state;
205
206		this_cpu_write(fpsimd_last_state, st);
207		st->cpu = smp_processor_id();
208	}
209	preempt_enable();
210}
211
212/*
213 * Invalidate live CPU copies of task t's FPSIMD state
214 */
215void fpsimd_flush_task_state(struct task_struct *t)
216{
217	t->thread.fpsimd_state.cpu = NR_CPUS;
218}
219
220#ifdef CONFIG_KERNEL_MODE_NEON
221
222static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate);
223static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate);
224
225/*
226 * Kernel-side NEON support functions
227 */
228void kernel_neon_begin_partial(u32 num_regs)
229{
230	if (in_interrupt()) {
231		struct fpsimd_partial_state *s = this_cpu_ptr(
232			in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
233
234		BUG_ON(num_regs > 32);
235		fpsimd_save_partial_state(s, roundup(num_regs, 2));
236	} else {
237		/*
238		 * Save the userland FPSIMD state if we have one and if we
239		 * haven't done so already. Clear fpsimd_last_state to indicate
240		 * that there is no longer userland FPSIMD state in the
241		 * registers.
242		 */
243		preempt_disable();
244		if (current->mm &&
245		    !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
246			fpsimd_save_state(&current->thread.fpsimd_state);
247		this_cpu_write(fpsimd_last_state, NULL);
248	}
249}
250EXPORT_SYMBOL(kernel_neon_begin_partial);
251
252void kernel_neon_end(void)
253{
254	if (in_interrupt()) {
255		struct fpsimd_partial_state *s = this_cpu_ptr(
256			in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
257		fpsimd_load_partial_state(s);
258	} else {
259		preempt_enable();
260	}
261}
262EXPORT_SYMBOL(kernel_neon_end);
263
264#endif /* CONFIG_KERNEL_MODE_NEON */
265
266#ifdef CONFIG_CPU_PM
267static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
268				  unsigned long cmd, void *v)
269{
270	switch (cmd) {
271	case CPU_PM_ENTER:
272		if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
273			fpsimd_save_state(&current->thread.fpsimd_state);
274		this_cpu_write(fpsimd_last_state, NULL);
275		break;
276	case CPU_PM_EXIT:
277		if (current->mm)
278			set_thread_flag(TIF_FOREIGN_FPSTATE);
279		break;
280	case CPU_PM_ENTER_FAILED:
281	default:
282		return NOTIFY_DONE;
283	}
284	return NOTIFY_OK;
285}
286
287static struct notifier_block fpsimd_cpu_pm_notifier_block = {
288	.notifier_call = fpsimd_cpu_pm_notifier,
289};
290
291static void fpsimd_pm_init(void)
292{
293	cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block);
294}
295
296#else
297static inline void fpsimd_pm_init(void) { }
298#endif /* CONFIG_CPU_PM */
299
300/*
301 * FP/SIMD support code initialisation.
302 */
303static int __init fpsimd_init(void)
304{
305	u64 pfr = read_cpuid(ID_AA64PFR0_EL1);
306
307	if (pfr & (0xf << 16)) {
308		pr_notice("Floating-point is not implemented\n");
309		return 0;
310	}
311	elf_hwcap |= HWCAP_FP;
312
313	if (pfr & (0xf << 20))
314		pr_notice("Advanced SIMD is not implemented\n");
315	else
316		elf_hwcap |= HWCAP_ASIMD;
317
318	fpsimd_pm_init();
319
320	return 0;
321}
322late_initcall(fpsimd_init);
323