xref: /openbmc/linux/arch/x86/kernel/process_32.c (revision 0edbfea5)
1 /*
2  *  Copyright (C) 1995  Linus Torvalds
3  *
4  *  Pentium III FXSR, SSE support
5  *	Gareth Hughes <gareth@valinux.com>, May 2000
6  */
7 
8 /*
9  * This file handles the architecture-dependent parts of process handling..
10  */
11 
12 #include <linux/cpu.h>
13 #include <linux/errno.h>
14 #include <linux/sched.h>
15 #include <linux/fs.h>
16 #include <linux/kernel.h>
17 #include <linux/mm.h>
18 #include <linux/elfcore.h>
19 #include <linux/smp.h>
20 #include <linux/stddef.h>
21 #include <linux/slab.h>
22 #include <linux/vmalloc.h>
23 #include <linux/user.h>
24 #include <linux/interrupt.h>
25 #include <linux/delay.h>
26 #include <linux/reboot.h>
27 #include <linux/mc146818rtc.h>
28 #include <linux/module.h>
29 #include <linux/kallsyms.h>
30 #include <linux/ptrace.h>
31 #include <linux/personality.h>
32 #include <linux/percpu.h>
33 #include <linux/prctl.h>
34 #include <linux/ftrace.h>
35 #include <linux/uaccess.h>
36 #include <linux/io.h>
37 #include <linux/kdebug.h>
38 
39 #include <asm/pgtable.h>
40 #include <asm/ldt.h>
41 #include <asm/processor.h>
42 #include <asm/fpu/internal.h>
43 #include <asm/desc.h>
44 #ifdef CONFIG_MATH_EMULATION
45 #include <asm/math_emu.h>
46 #endif
47 
48 #include <linux/err.h>
49 
50 #include <asm/tlbflush.h>
51 #include <asm/cpu.h>
52 #include <asm/idle.h>
53 #include <asm/syscalls.h>
54 #include <asm/debugreg.h>
55 #include <asm/switch_to.h>
56 #include <asm/vm86.h>
57 
58 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
59 asmlinkage void ret_from_kernel_thread(void) __asm__("ret_from_kernel_thread");
60 
61 /*
62  * Return saved PC of a blocked thread.
63  */
64 unsigned long thread_saved_pc(struct task_struct *tsk)
65 {
66 	return ((unsigned long *)tsk->thread.sp)[3];
67 }
68 
69 void __show_regs(struct pt_regs *regs, int all)
70 {
71 	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
72 	unsigned long d0, d1, d2, d3, d6, d7;
73 	unsigned long sp;
74 	unsigned short ss, gs;
75 
76 	if (user_mode(regs)) {
77 		sp = regs->sp;
78 		ss = regs->ss & 0xffff;
79 		gs = get_user_gs(regs);
80 	} else {
81 		sp = kernel_stack_pointer(regs);
82 		savesegment(ss, ss);
83 		savesegment(gs, gs);
84 	}
85 
86 	printk(KERN_DEFAULT "EIP: %04x:[<%08lx>] EFLAGS: %08lx CPU: %d\n",
87 			(u16)regs->cs, regs->ip, regs->flags,
88 			smp_processor_id());
89 	print_symbol("EIP is at %s\n", regs->ip);
90 
91 	printk(KERN_DEFAULT "EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
92 		regs->ax, regs->bx, regs->cx, regs->dx);
93 	printk(KERN_DEFAULT "ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
94 		regs->si, regs->di, regs->bp, sp);
95 	printk(KERN_DEFAULT " DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x\n",
96 	       (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss);
97 
98 	if (!all)
99 		return;
100 
101 	cr0 = read_cr0();
102 	cr2 = read_cr2();
103 	cr3 = read_cr3();
104 	cr4 = __read_cr4_safe();
105 	printk(KERN_DEFAULT "CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
106 			cr0, cr2, cr3, cr4);
107 
108 	get_debugreg(d0, 0);
109 	get_debugreg(d1, 1);
110 	get_debugreg(d2, 2);
111 	get_debugreg(d3, 3);
112 	get_debugreg(d6, 6);
113 	get_debugreg(d7, 7);
114 
115 	/* Only print out debug registers if they are in their non-default state. */
116 	if ((d0 == 0) && (d1 == 0) && (d2 == 0) && (d3 == 0) &&
117 	    (d6 == DR6_RESERVED) && (d7 == 0x400))
118 		return;
119 
120 	printk(KERN_DEFAULT "DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
121 			d0, d1, d2, d3);
122 	printk(KERN_DEFAULT "DR6: %08lx DR7: %08lx\n",
123 			d6, d7);
124 }
125 
126 void release_thread(struct task_struct *dead_task)
127 {
128 	BUG_ON(dead_task->mm);
129 	release_vm86_irqs(dead_task);
130 }
131 
132 int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
133 	unsigned long arg, struct task_struct *p, unsigned long tls)
134 {
135 	struct pt_regs *childregs = task_pt_regs(p);
136 	struct task_struct *tsk;
137 	int err;
138 
139 	p->thread.sp = (unsigned long) childregs;
140 	p->thread.sp0 = (unsigned long) (childregs+1);
141 	memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
142 
143 	if (unlikely(p->flags & PF_KTHREAD)) {
144 		/* kernel thread */
145 		memset(childregs, 0, sizeof(struct pt_regs));
146 		p->thread.ip = (unsigned long) ret_from_kernel_thread;
147 		task_user_gs(p) = __KERNEL_STACK_CANARY;
148 		childregs->ds = __USER_DS;
149 		childregs->es = __USER_DS;
150 		childregs->fs = __KERNEL_PERCPU;
151 		childregs->bx = sp;	/* function */
152 		childregs->bp = arg;
153 		childregs->orig_ax = -1;
154 		childregs->cs = __KERNEL_CS | get_kernel_rpl();
155 		childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED;
156 		p->thread.io_bitmap_ptr = NULL;
157 		return 0;
158 	}
159 	*childregs = *current_pt_regs();
160 	childregs->ax = 0;
161 	if (sp)
162 		childregs->sp = sp;
163 
164 	p->thread.ip = (unsigned long) ret_from_fork;
165 	task_user_gs(p) = get_user_gs(current_pt_regs());
166 
167 	p->thread.io_bitmap_ptr = NULL;
168 	tsk = current;
169 	err = -ENOMEM;
170 
171 	if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
172 		p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
173 						IO_BITMAP_BYTES, GFP_KERNEL);
174 		if (!p->thread.io_bitmap_ptr) {
175 			p->thread.io_bitmap_max = 0;
176 			return -ENOMEM;
177 		}
178 		set_tsk_thread_flag(p, TIF_IO_BITMAP);
179 	}
180 
181 	err = 0;
182 
183 	/*
184 	 * Set a new TLS for the child thread?
185 	 */
186 	if (clone_flags & CLONE_SETTLS)
187 		err = do_set_thread_area(p, -1,
188 			(struct user_desc __user *)tls, 0);
189 
190 	if (err && p->thread.io_bitmap_ptr) {
191 		kfree(p->thread.io_bitmap_ptr);
192 		p->thread.io_bitmap_max = 0;
193 	}
194 	return err;
195 }
196 
197 void
198 start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
199 {
200 	set_user_gs(regs, 0);
201 	regs->fs		= 0;
202 	regs->ds		= __USER_DS;
203 	regs->es		= __USER_DS;
204 	regs->ss		= __USER_DS;
205 	regs->cs		= __USER_CS;
206 	regs->ip		= new_ip;
207 	regs->sp		= new_sp;
208 	regs->flags		= X86_EFLAGS_IF;
209 	force_iret();
210 }
211 EXPORT_SYMBOL_GPL(start_thread);
212 
213 
214 /*
215  *	switch_to(x,y) should switch tasks from x to y.
216  *
217  * We fsave/fwait so that an exception goes off at the right time
218  * (as a call from the fsave or fwait in effect) rather than to
219  * the wrong process. Lazy FP saving no longer makes any sense
220  * with modern CPU's, and this simplifies a lot of things (SMP
221  * and UP become the same).
222  *
223  * NOTE! We used to use the x86 hardware context switching. The
224  * reason for not using it any more becomes apparent when you
225  * try to recover gracefully from saved state that is no longer
226  * valid (stale segment register values in particular). With the
227  * hardware task-switch, there is no way to fix up bad state in
228  * a reasonable manner.
229  *
230  * The fact that Intel documents the hardware task-switching to
231  * be slow is a fairly red herring - this code is not noticeably
232  * faster. However, there _is_ some room for improvement here,
233  * so the performance issues may eventually be a valid point.
234  * More important, however, is the fact that this allows us much
235  * more flexibility.
236  *
237  * The return value (in %ax) will be the "prev" task after
238  * the task-switch, and shows up in ret_from_fork in entry.S,
239  * for example.
240  */
241 __visible __notrace_funcgraph struct task_struct *
242 __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
243 {
244 	struct thread_struct *prev = &prev_p->thread,
245 			     *next = &next_p->thread;
246 	struct fpu *prev_fpu = &prev->fpu;
247 	struct fpu *next_fpu = &next->fpu;
248 	int cpu = smp_processor_id();
249 	struct tss_struct *tss = &per_cpu(cpu_tss, cpu);
250 	fpu_switch_t fpu_switch;
251 
252 	/* never put a printk in __switch_to... printk() calls wake_up*() indirectly */
253 
254 	fpu_switch = switch_fpu_prepare(prev_fpu, next_fpu, cpu);
255 
256 	/*
257 	 * Save away %gs. No need to save %fs, as it was saved on the
258 	 * stack on entry.  No need to save %es and %ds, as those are
259 	 * always kernel segments while inside the kernel.  Doing this
260 	 * before setting the new TLS descriptors avoids the situation
261 	 * where we temporarily have non-reloadable segments in %fs
262 	 * and %gs.  This could be an issue if the NMI handler ever
263 	 * used %fs or %gs (it does not today), or if the kernel is
264 	 * running inside of a hypervisor layer.
265 	 */
266 	lazy_save_gs(prev->gs);
267 
268 	/*
269 	 * Load the per-thread Thread-Local Storage descriptor.
270 	 */
271 	load_TLS(next, cpu);
272 
273 	/*
274 	 * Restore IOPL if needed.  In normal use, the flags restore
275 	 * in the switch assembly will handle this.  But if the kernel
276 	 * is running virtualized at a non-zero CPL, the popf will
277 	 * not restore flags, so it must be done in a separate step.
278 	 */
279 	if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
280 		set_iopl_mask(next->iopl);
281 
282 	/*
283 	 * Now maybe handle debug registers and/or IO bitmaps
284 	 */
285 	if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV ||
286 		     task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
287 		__switch_to_xtra(prev_p, next_p, tss);
288 
289 	/*
290 	 * Leave lazy mode, flushing any hypercalls made here.
291 	 * This must be done before restoring TLS segments so
292 	 * the GDT and LDT are properly updated, and must be
293 	 * done before fpu__restore(), so the TS bit is up
294 	 * to date.
295 	 */
296 	arch_end_context_switch(next_p);
297 
298 	/*
299 	 * Reload esp0 and cpu_current_top_of_stack.  This changes
300 	 * current_thread_info().
301 	 */
302 	load_sp0(tss, next);
303 	this_cpu_write(cpu_current_top_of_stack,
304 		       (unsigned long)task_stack_page(next_p) +
305 		       THREAD_SIZE);
306 
307 	/*
308 	 * Restore %gs if needed (which is common)
309 	 */
310 	if (prev->gs | next->gs)
311 		lazy_load_gs(next->gs);
312 
313 	switch_fpu_finish(next_fpu, fpu_switch);
314 
315 	this_cpu_write(current_task, next_p);
316 
317 	return prev_p;
318 }
319