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2023-12-08 01573e231f18eb2d99162747186f59511f56b64d 
 kernel/arch/x86/kernel/fpu/core.c
....@@ -1,3 +1,4 @@
1
+// SPDX-License-Identifier: GPL-2.0-only
12 /*
23  *  Copyright (C) 1994 Linus Torvalds
34  *
....@@ -42,18 +43,6 @@
4243  */
4344 DEFINE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
4445 
45
-static void kernel_fpu_disable(void)
46
-{
47
-	WARN_ON_FPU(this_cpu_read(in_kernel_fpu));
48
-	this_cpu_write(in_kernel_fpu, true);
49
-}
50
-
51
-static void kernel_fpu_enable(void)
52
-{
53
-	WARN_ON_FPU(!this_cpu_read(in_kernel_fpu));
54
-	this_cpu_write(in_kernel_fpu, false);
55
-}
56
-
5746 static bool kernel_fpu_disabled(void)
5847 {
5948 	return this_cpu_read(in_kernel_fpu);
....@@ -93,48 +82,94 @@
9382 }
9483 EXPORT_SYMBOL(irq_fpu_usable);
9584 
96
-static void __kernel_fpu_begin(void)
85
+/*
86
+ * These must be called with preempt disabled. Returns
87
+ * 'true' if the FPU state is still intact and we can
88
+ * keep registers active.
89
+ *
90
+ * The legacy FNSAVE instruction cleared all FPU state
91
+ * unconditionally, so registers are essentially destroyed.
92
+ * Modern FPU state can be kept in registers, if there are
93
+ * no pending FP exceptions.
94
+ */
95
+int copy_fpregs_to_fpstate(struct fpu *fpu)
9796 {
98
-	struct fpu *fpu = &current->thread.fpu;
97
+	if (likely(use_xsave())) {
98
+		copy_xregs_to_kernel(&fpu->state.xsave);
99
+
100
+		/*
101
+		 * AVX512 state is tracked here because its use is
102
+		 * known to slow the max clock speed of the core.
103
+		 */
104
+		if (fpu->state.xsave.header.xfeatures & XFEATURE_MASK_AVX512)
105
+			fpu->avx512_timestamp = jiffies;
106
+		return 1;
107
+	}
108
+
109
+	if (likely(use_fxsr())) {
110
+		copy_fxregs_to_kernel(fpu);
111
+		return 1;
112
+	}
113
+
114
+	/*
115
+	 * Legacy FPU register saving, FNSAVE always clears FPU registers,
116
+	 * so we have to mark them inactive:
117
+	 */
118
+	asm volatile("fnsave %[fp]; fwait" : [fp] "=m" (fpu->state.fsave));
119
+
120
+	return 0;
121
+}
122
+EXPORT_SYMBOL(copy_fpregs_to_fpstate);
123
+
124
+void kernel_fpu_begin_mask(unsigned int kfpu_mask)
125
+{
126
+	preempt_disable();
99127 
100128 	WARN_ON_FPU(!irq_fpu_usable());
129
+	WARN_ON_FPU(this_cpu_read(in_kernel_fpu));
101130 
102
-	kernel_fpu_disable();
131
+	this_cpu_write(in_kernel_fpu, true);
103132 
104
-	if (fpu->initialized) {
133
+	if (!(current->flags & PF_KTHREAD) &&
134
+	    !test_thread_flag(TIF_NEED_FPU_LOAD)) {
135
+		set_thread_flag(TIF_NEED_FPU_LOAD);
105136 		/*
106137 		 * Ignore return value -- we don't care if reg state
107138 		 * is clobbered.
108139 		 */
109
-		copy_fpregs_to_fpstate(fpu);
110
-	} else {
111
-		__cpu_invalidate_fpregs_state();
140
+		copy_fpregs_to_fpstate(&current->thread.fpu);
112141 	}
142
+	__cpu_invalidate_fpregs_state();
143
+
144
+	/* Put sane initial values into the control registers. */
145
+	if (likely(kfpu_mask & KFPU_MXCSR) && boot_cpu_has(X86_FEATURE_XMM))
146
+		ldmxcsr(MXCSR_DEFAULT);
147
+
148
+	if (unlikely(kfpu_mask & KFPU_387) && boot_cpu_has(X86_FEATURE_FPU))
149
+		asm volatile ("fninit");
113150 }
114
-
115
-static void __kernel_fpu_end(void)
116
-{
117
-	struct fpu *fpu = &current->thread.fpu;
118
-
119
-	if (fpu->initialized)
120
-		copy_kernel_to_fpregs(&fpu->state);
121
-
122
-	kernel_fpu_enable();
123
-}
124
-
125
-void kernel_fpu_begin(void)
126
-{
127
-	preempt_disable();
128
-	__kernel_fpu_begin();
129
-}
130
-EXPORT_SYMBOL_GPL(kernel_fpu_begin);
151
+EXPORT_SYMBOL_GPL(kernel_fpu_begin_mask);
131152 
132153 void kernel_fpu_end(void)
133154 {
134
-	__kernel_fpu_end();
155
+	WARN_ON_FPU(!this_cpu_read(in_kernel_fpu));
156
+
157
+	this_cpu_write(in_kernel_fpu, false);
135158 	preempt_enable();
136159 }
137160 EXPORT_SYMBOL_GPL(kernel_fpu_end);
161
+
162
+void kernel_fpu_resched(void)
163
+{
164
+	WARN_ON_FPU(!this_cpu_read(in_kernel_fpu));
165
+
166
+	if (should_resched(PREEMPT_OFFSET)) {
167
+		kernel_fpu_end();
168
+		cond_resched();
169
+		kernel_fpu_begin();
170
+	}
171
+}
172
+EXPORT_SYMBOL_GPL(kernel_fpu_resched);
138173 
139174 /*
140175  * Save the FPU state (mark it for reload if necessary):
....@@ -145,17 +180,18 @@
145180 {
146181 	WARN_ON_FPU(fpu != &current->thread.fpu);
147182 
148
-	preempt_disable();
183
+	fpregs_lock();
149184 	trace_x86_fpu_before_save(fpu);
150
-	if (fpu->initialized) {
185
+
186
+	if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
151187 		if (!copy_fpregs_to_fpstate(fpu)) {
152188 			copy_kernel_to_fpregs(&fpu->state);
153189 		}
154190 	}
191
+
155192 	trace_x86_fpu_after_save(fpu);
156
-	preempt_enable();
193
+	fpregs_unlock();
157194 }
158
-EXPORT_SYMBOL_GPL(fpu__save);
159195 
160196 /*
161197  * Legacy x87 fpstate state init:
....@@ -186,11 +222,14 @@
186222 }
187223 EXPORT_SYMBOL_GPL(fpstate_init);
188224 
189
-int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
225
+int fpu__copy(struct task_struct *dst, struct task_struct *src)
190226 {
227
+	struct fpu *dst_fpu = &dst->thread.fpu;
228
+	struct fpu *src_fpu = &src->thread.fpu;
229
+
191230 	dst_fpu->last_cpu = -1;
192231 
193
-	if (!src_fpu->initialized || !static_cpu_has(X86_FEATURE_FPU))
232
+	if (!static_cpu_has(X86_FEATURE_FPU))
194233 		return 0;
195234 
196235 	WARN_ON_FPU(src_fpu != &current->thread.fpu);
....@@ -202,16 +241,23 @@
202241 	memset(&dst_fpu->state.xsave, 0, fpu_kernel_xstate_size);
203242 
204243 	/*
205
-	 * Save current FPU registers directly into the child
206
-	 * FPU context, without any memory-to-memory copying.
244
+	 * If the FPU registers are not current just memcpy() the state.
245
+	 * Otherwise save current FPU registers directly into the child's FPU
246
+	 * context, without any memory-to-memory copying.
207247 	 *
208248 	 * ( The function 'fails' in the FNSAVE case, which destroys
209
-	 *   register contents so we have to copy them back. )
249
+	 *   register contents so we have to load them back. )
210250 	 */
211
-	if (!copy_fpregs_to_fpstate(dst_fpu)) {
212
-		memcpy(&src_fpu->state, &dst_fpu->state, fpu_kernel_xstate_size);
213
-		copy_kernel_to_fpregs(&src_fpu->state);
214
-	}
251
+	fpregs_lock();
252
+	if (test_thread_flag(TIF_NEED_FPU_LOAD))
253
+		memcpy(&dst_fpu->state, &src_fpu->state, fpu_kernel_xstate_size);
254
+
255
+	else if (!copy_fpregs_to_fpstate(dst_fpu))
256
+		copy_kernel_to_fpregs(&dst_fpu->state);
257
+
258
+	fpregs_unlock();
259
+
260
+	set_tsk_thread_flag(dst, TIF_NEED_FPU_LOAD);
215261 
216262 	trace_x86_fpu_copy_src(src_fpu);
217263 	trace_x86_fpu_copy_dst(dst_fpu);
....@@ -223,20 +269,14 @@
223269  * Activate the current task's in-memory FPU context,
224270  * if it has not been used before:
225271  */
226
-void fpu__initialize(struct fpu *fpu)
272
+static void fpu__initialize(struct fpu *fpu)
227273 {
228274 	WARN_ON_FPU(fpu != &current->thread.fpu);
229275 
230
-	if (!fpu->initialized) {
231
-		fpstate_init(&fpu->state);
232
-		trace_x86_fpu_init_state(fpu);
233
-
234
-		trace_x86_fpu_activate_state(fpu);
235
-		/* Safe to do for the current task: */
236
-		fpu->initialized = 1;
237
-	}
276
+	set_thread_flag(TIF_NEED_FPU_LOAD);
277
+	fpstate_init(&fpu->state);
278
+	trace_x86_fpu_init_state(fpu);
238279 }
239
-EXPORT_SYMBOL_GPL(fpu__initialize);
240280 
241281 /*
242282  * This function must be called before we read a task's fpstate.
....@@ -248,32 +288,20 @@
248288  *
249289  * - or it's called for stopped tasks (ptrace), in which case the
250290  *   registers were already saved by the context-switch code when
251
- *   the task scheduled out - we only have to initialize the registers
252
- *   if they've never been initialized.
291
+ *   the task scheduled out.
253292  *
254293  * If the task has used the FPU before then save it.
255294  */
256295 void fpu__prepare_read(struct fpu *fpu)
257296 {
258
-	if (fpu == &current->thread.fpu) {
297
+	if (fpu == &current->thread.fpu)
259298 		fpu__save(fpu);
260
-	} else {
261
-		if (!fpu->initialized) {
262
-			fpstate_init(&fpu->state);
263
-			trace_x86_fpu_init_state(fpu);
264
-
265
-			trace_x86_fpu_activate_state(fpu);
266
-			/* Safe to do for current and for stopped child tasks: */
267
-			fpu->initialized = 1;
268
-		}
269
-	}
270299 }
271300 
272301 /*
273302  * This function must be called before we write a task's fpstate.
274303  *
275
- * If the task has used the FPU before then invalidate any cached FPU registers.
276
- * If the task has not used the FPU before then initialize its fpstate.
304
+ * Invalidate any cached FPU registers.
277305  *
278306  * After this function call, after registers in the fpstate are
279307  * modified and the child task has woken up, the child task will
....@@ -290,42 +318,9 @@
290318 	 */
291319 	WARN_ON_FPU(fpu == &current->thread.fpu);
292320 
293
-	if (fpu->initialized) {
294
-		/* Invalidate any cached state: */
295
-		__fpu_invalidate_fpregs_state(fpu);
296
-	} else {
297
-		fpstate_init(&fpu->state);
298
-		trace_x86_fpu_init_state(fpu);
299
-
300
-		trace_x86_fpu_activate_state(fpu);
301
-		/* Safe to do for stopped child tasks: */
302
-		fpu->initialized = 1;
303
-	}
321
+	/* Invalidate any cached state: */
322
+	__fpu_invalidate_fpregs_state(fpu);
304323 }
305
-
306
-/*
307
- * 'fpu__restore()' is called to copy FPU registers from
308
- * the FPU fpstate to the live hw registers and to activate
309
- * access to the hardware registers, so that FPU instructions
310
- * can be used afterwards.
311
- *
312
- * Must be called with kernel preemption disabled (for example
313
- * with local interrupts disabled, as it is in the case of
314
- * do_device_not_available()).
315
- */
316
-void fpu__restore(struct fpu *fpu)
317
-{
318
-	fpu__initialize(fpu);
319
-
320
-	/* Avoid __kernel_fpu_begin() right after fpregs_activate() */
321
-	kernel_fpu_disable();
322
-	trace_x86_fpu_before_restore(fpu);
323
-	fpregs_activate(fpu);
324
-	copy_kernel_to_fpregs(&fpu->state);
325
-	trace_x86_fpu_after_restore(fpu);
326
-	kernel_fpu_enable();
327
-}
328
-EXPORT_SYMBOL_GPL(fpu__restore);
329324 
330325 /*
331326  * Drops current FPU state: deactivates the fpregs and
....@@ -341,16 +336,12 @@
341336 	preempt_disable();
342337 
343338 	if (fpu == &current->thread.fpu) {
344
-		if (fpu->initialized) {
345
-			/* Ignore delayed exceptions from user space */
346
-			asm volatile("1: fwait\n"
347
-				     "2:\n"
348
-				     _ASM_EXTABLE(1b, 2b));
349
-			fpregs_deactivate(fpu);
350
-		}
339
+		/* Ignore delayed exceptions from user space */
340
+		asm volatile("1: fwait\n"
341
+			     "2:\n"
342
+			     _ASM_EXTABLE(1b, 2b));
343
+		fpregs_deactivate(fpu);
351344 	}
352
-
353
-	fpu->initialized = 0;
354345 
355346 	trace_x86_fpu_dropped(fpu);
356347 
....@@ -358,13 +349,13 @@
358349 }
359350 
360351 /*
361
- * Clear FPU registers by setting them up from
362
- * the init fpstate:
352
+ * Clear FPU registers by setting them up from the init fpstate.
353
+ * Caller must do fpregs_[un]lock() around it.
363354  */
364
-static inline void copy_init_fpstate_to_fpregs(void)
355
+static inline void copy_init_fpstate_to_fpregs(u64 features_mask)
365356 {
366357 	if (use_xsave())
367
-		copy_kernel_to_xregs(&init_fpstate.xsave, -1);
358
+		copy_kernel_to_xregs(&init_fpstate.xsave, features_mask);
368359 	else if (static_cpu_has(X86_FEATURE_FXSR))
369360 		copy_kernel_to_fxregs(&init_fpstate.fxsave);
370361 	else
....@@ -380,24 +371,82 @@
380371  * Called by sys_execve(), by the signal handler code and by various
381372  * error paths.
382373  */
383
-void fpu__clear(struct fpu *fpu)
374
+static void fpu__clear(struct fpu *fpu, bool user_only)
384375 {
385
-	WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */
376
+	WARN_ON_FPU(fpu != &current->thread.fpu);
386377 
387
-	fpu__drop(fpu);
388
-
389
-	/*
390
-	 * Make sure fpstate is cleared and initialized.
391
-	 */
392
-	if (static_cpu_has(X86_FEATURE_FPU)) {
393
-		preempt_disable();
378
+	if (!static_cpu_has(X86_FEATURE_FPU)) {
379
+		fpu__drop(fpu);
394380 		fpu__initialize(fpu);
395
-		user_fpu_begin();
396
-		copy_init_fpstate_to_fpregs();
397
-		preempt_enable();
381
+		return;
398382 	}
383
+
384
+	fpregs_lock();
385
+
386
+	if (user_only) {
387
+		if (!fpregs_state_valid(fpu, smp_processor_id()) &&
388
+		    xfeatures_mask_supervisor())
389
+			copy_kernel_to_xregs(&fpu->state.xsave,
390
+					     xfeatures_mask_supervisor());
391
+		copy_init_fpstate_to_fpregs(xfeatures_mask_user());
392
+	} else {
393
+		copy_init_fpstate_to_fpregs(xfeatures_mask_all);
394
+	}
395
+
396
+	fpregs_mark_activate();
397
+	fpregs_unlock();
399398 }
400399 
400
+void fpu__clear_user_states(struct fpu *fpu)
401
+{
402
+	fpu__clear(fpu, true);
403
+}
404
+
405
+void fpu__clear_all(struct fpu *fpu)
406
+{
407
+	fpu__clear(fpu, false);
408
+}
409
+
410
+/*
411
+ * Load FPU context before returning to userspace.
412
+ */
413
+void switch_fpu_return(void)
414
+{
415
+	if (!static_cpu_has(X86_FEATURE_FPU))
416
+		return;
417
+
418
+	__fpregs_load_activate();
419
+}
420
+EXPORT_SYMBOL_GPL(switch_fpu_return);
421
+
422
+#ifdef CONFIG_X86_DEBUG_FPU
423
+/*
424
+ * If current FPU state according to its tracking (loaded FPU context on this
425
+ * CPU) is not valid then we must have TIF_NEED_FPU_LOAD set so the context is
426
+ * loaded on return to userland.
427
+ */
428
+void fpregs_assert_state_consistent(void)
429
+{
430
+	struct fpu *fpu = &current->thread.fpu;
431
+
432
+	if (test_thread_flag(TIF_NEED_FPU_LOAD))
433
+		return;
434
+
435
+	WARN_ON_FPU(!fpregs_state_valid(fpu, smp_processor_id()));
436
+}
437
+EXPORT_SYMBOL_GPL(fpregs_assert_state_consistent);
438
+#endif
439
+
440
+void fpregs_mark_activate(void)
441
+{
442
+	struct fpu *fpu = &current->thread.fpu;
443
+
444
+	fpregs_activate(fpu);
445
+	fpu->last_cpu = smp_processor_id();
446
+	clear_thread_flag(TIF_NEED_FPU_LOAD);
447
+}
448
+EXPORT_SYMBOL_GPL(fpregs_mark_activate);
449
+
401450 /*
402451  * x87 math exception handling:
403452  */