2 * Copyright (c) 1990 The Regents of the University of California.
4 * LWKT threads Copyright (c) 2003 Matthew Dillon
6 * This code is derived from software contributed to Berkeley by
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. All advertising materials mentioning features or use of this software
18 * must display the following acknowledgement:
19 * This product includes software developed by the University of
20 * California, Berkeley and its contributors.
21 * 4. Neither the name of the University nor the names of its contributors
22 * may be used to endorse or promote products derived from this software
23 * without specific prior written permission.
25 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 * $FreeBSD: src/sys/i386/i386/swtch.s,v 1.89.2.10 2003/01/23 03:36:24 ps Exp $
38 * $DragonFly: src/sys/i386/i386/Attic/swtch.s,v 1.28 2003/09/25 23:49:03 dillon Exp $
42 #include "opt_user_ldt.h"
44 #include <sys/rtprio.h>
46 #include <machine/asmacros.h>
47 #include <machine/ipl.h>
50 #include <machine/pmap.h>
51 #include <machine/smptests.h> /** GRAB_LOPRIO */
52 #include <machine/apic.h>
53 #include <machine/lock.h>
59 #define MPLOCKED lock ;
68 #if defined(SWTCH_OPTIM_STATS)
69 .globl swtch_optim_stats, tlb_flush_count
70 swtch_optim_stats: .long 0 /* number of _swtch_optims */
71 tlb_flush_count: .long 0
78 * cpu_heavy_switch(next_thread)
80 * Switch from the current thread to a new thread. This entry
81 * is normally called via the thread->td_switch function, and will
82 * only be called when the current thread is a heavy weight process.
84 * Some instructions have been reordered to reduce pipeline stalls.
86 * YYY disable interrupts once giant is removed.
88 ENTRY(cpu_heavy_switch)
92 movl PCPU(curthread),%ecx
93 movl (%esp),%eax /* (reorder optimization) */
94 movl TD_PCB(%ecx),%edx /* EDX = PCB */
95 movl %eax,PCB_EIP(%edx) /* return PC may be modified */
96 movl %ebx,PCB_EBX(%edx)
97 movl %esp,PCB_ESP(%edx)
98 movl %ebp,PCB_EBP(%edx)
99 movl %esi,PCB_ESI(%edx)
100 movl %edi,PCB_EDI(%edx)
101 movl %gs,PCB_GS(%edx)
103 movl %ecx,%ebx /* EBX = curthread */
104 movl TD_PROC(%ecx),%ecx
105 movl PCPU(cpuid), %eax
106 movl P_VMSPACE(%ecx), %ecx /* ECX = vmspace */
107 MPLOCKED btrl %eax, VM_PMAP+PM_ACTIVE(%ecx)
110 * Push the LWKT switch restore function, which resumes a heavy
111 * weight process. Note that the LWKT switcher is based on
112 * TD_SP, while the heavy weight process switcher is based on
113 * PCB_ESP. TD_SP is usually two ints pushed relative to
114 * PCB_ESP. We push the flags for later restore by cpu_heavy_restore.
117 pushl $cpu_heavy_restore
118 movl %esp,TD_SP(%ebx)
121 * Save debug regs if necessary
123 movb PCB_FLAGS(%edx),%al
125 jz 1f /* no, skip over */
126 movl %dr7,%eax /* yes, do the save */
127 movl %eax,PCB_DR7(%edx)
128 andl $0x0000fc00, %eax /* disable all watchpoints */
131 movl %eax,PCB_DR6(%edx)
133 movl %eax,PCB_DR3(%edx)
135 movl %eax,PCB_DR2(%edx)
137 movl %eax,PCB_DR1(%edx)
139 movl %eax,PCB_DR0(%edx)
143 * Save the FP state if we have used the FP. Note that calling
144 * npxsave will NULL out PCPU(npxthread).
147 cmpl %ebx,PCPU(npxthread)
149 addl $PCB_SAVEFPU,%edx
151 call npxsave /* do it in a big C function */
152 addl $4,%esp /* EAX, ECX, EDX trashed */
154 #endif /* NNPX > 0 */
157 * Switch to the next thread, which was passed as an argument
158 * to cpu_heavy_switch(). Due to the eflags and switch-restore
159 * function we pushed, the argument is at 12(%esp). Set the current
160 * thread, load the stack pointer, and 'ret' into the switch-restore
163 * The switch restore function expects the new thread to be in %eax
164 * and the old one to be in %ebx.
166 * There is a one-instruction window where curthread is the new
167 * thread but %esp still points to the old thread's stack, but
168 * we are protected by a critical section so it is ok.
170 movl 12(%esp),%eax /* EAX = newtd, EBX = oldtd */
171 movl %eax,PCPU(curthread)
172 movl TD_SP(%eax),%esp
178 * The switch function is changed to this when a thread is going away
179 * for good. We have to ensure that the MMU state is not cached, and
180 * we don't bother saving the existing thread state before switching.
182 * At this point we are in a critical section and this cpu owns the
183 * thread's token, which serves as an interlock until the switchout is
186 ENTRY(cpu_exit_switch)
188 * Get us out of the vmspace
196 movl PCPU(curthread),%ebx
198 * Switch to the next thread. RET into the restore function, which
199 * expects the new thread in EAX and the old in EBX.
201 * There is a one-instruction window where curthread is the new
202 * thread but %esp still points to the old thread's stack, but
203 * we are protected by a critical section so it is ok.
206 movl %eax,PCPU(curthread)
207 movl TD_SP(%eax),%esp
211 * cpu_heavy_restore() (current thread in %eax on entry)
213 * Restore the thread after an LWKT switch. This entry is normally
214 * called via the LWKT switch restore function, which was pulled
215 * off the thread stack and jumped to.
217 * This entry is only called if the thread was previously saved
218 * using cpu_heavy_switch() (the heavy weight process thread switcher),
219 * or when a new process is initially scheduled. The first thing we
220 * do is clear the TDF_RUNNING bit in the old thread and set it in the
223 * YYY theoretically we do not have to restore everything here, a lot
224 * of this junk can wait until we return to usermode. But for now
225 * we restore everything.
227 * YYY the PCB crap is really crap, it makes startup a bitch because
228 * we can't switch away.
230 * YYY note: spl check is done in mi_switch when it splx()'s.
233 ENTRY(cpu_heavy_restore)
235 movl TD_PCB(%eax),%edx /* EDX = PCB */
236 movl TD_PROC(%eax),%ecx
239 * A heavy weight process will normally be in an SRUN state
240 * but can also be preempted while it is entering a SZOMB
243 cmpb $SRUN,P_STAT(%ecx)
245 cmpb $SZOMB,P_STAT(%ecx)
250 #if defined(SWTCH_OPTIM_STATS)
251 incl _swtch_optim_stats
254 * Tell the pmap that our cpu is using the VMSPACE now. We cannot
255 * safely test/reload %cr3 until after we have set the bit in the
256 * pmap (remember, we do not hold the MP lock in the switch code).
258 movl P_VMSPACE(%ecx), %ecx /* ECX = vmspace */
259 movl PCPU(cpuid), %esi
260 MPLOCKED btsl %esi, VM_PMAP+PM_ACTIVE(%ecx)
263 * Restore the MMU address space. If it is the same as the last
264 * thread we don't have to invalidate the tlb (i.e. reload cr3).
265 * YYY which naturally also means that the PM_ACTIVE bit had better
266 * already have been set before we set it above, check? YYY
269 movl PCB_CR3(%edx),%ecx
272 #if defined(SWTCH_OPTIM_STATS)
273 decl _swtch_optim_stats
274 incl _tlb_flush_count
279 * Clear TDF_RUNNING flag in old thread only after cleaning up
280 * %cr3. The target thread is already protected by being TDF_RUNQ
281 * so setting TDF_RUNNING isn't as big a deal.
283 andl $~TDF_RUNNING,TD_FLAGS(%ebx)
284 orl $TDF_RUNNING,TD_FLAGS(%eax)
287 * Deal with the PCB extension, restore the private tss
289 movl PCB_EXT(%edx),%edi /* check for a PCB extension */
290 movl $1,%ebx /* maybe mark use of a private tss */
295 * Going back to the common_tss. We may need to update TSS_ESP0
296 * which sets the top of the supervisor stack when entering from
297 * usermode. The PCB is at the top of the stack but we need another
298 * 16 bytes to take vm86 into account.
301 movl %ebx, PCPU(common_tss) + TSS_ESP0
303 cmpl $0,PCPU(private_tss) /* don't have to reload if */
304 je 3f /* already using the common TSS */
306 subl %ebx,%ebx /* unmark use of private tss */
309 * Get the address of the common TSS descriptor for the ltr.
310 * There is no way to get the address of a segment-accessed variable
311 * so we store a self-referential pointer at the base of the per-cpu
312 * data area and add the appropriate offset.
314 movl $gd_common_tssd, %edi
318 * Move the correct TSS descriptor into the GDT slot, then reload
322 movl %ebx,PCPU(private_tss) /* mark/unmark private tss */
323 movl PCPU(tss_gdt), %ebx /* entry in GDT */
328 movl $GPROC0_SEL*8, %esi /* GSEL(entry, SEL_KPL) */
333 * Restore general registers.
335 movl PCB_EBX(%edx),%ebx
336 movl PCB_ESP(%edx),%esp
337 movl PCB_EBP(%edx),%ebp
338 movl PCB_ESI(%edx),%esi
339 movl PCB_EDI(%edx),%edi
340 movl PCB_EIP(%edx),%eax
344 * Restore the user LDT if we have one
347 cmpl $0, PCB_USERLDT(%edx)
349 movl _default_ldt,%eax
350 cmpl PCPU(currentldt),%eax
353 movl %eax,PCPU(currentldt)
361 * Restore the %gs segment register, which must be done after
362 * loading the user LDT. Since user processes can modify the
363 * register via procfs, this may result in a fault which is
364 * detected by checking the fault address against cpu_switch_load_gs
365 * in i386/i386/trap.c
367 .globl cpu_switch_load_gs
369 movl PCB_GS(%edx),%gs
372 * Restore the DEBUG register state if necessary.
374 movb PCB_FLAGS(%edx),%al
376 jz 1f /* no, skip over */
377 movl PCB_DR6(%edx),%eax /* yes, do the restore */
379 movl PCB_DR3(%edx),%eax
381 movl PCB_DR2(%edx),%eax
383 movl PCB_DR1(%edx),%eax
385 movl PCB_DR0(%edx),%eax
387 movl %dr7,%eax /* load dr7 so as not to disturb */
388 andl $0x0000fc00,%eax /* reserved bits */
390 movl PCB_DR7(%edx),%ebx
391 andl $~0x0000fc00,%ebx
403 sw0_2: .asciz "cpu_switch: not SRUN"
407 * Update pcb, saving current processor state.
413 /* caller's return address - child won't execute this routine */
415 movl %eax,PCB_EIP(%ecx)
418 movl %eax,PCB_CR3(%ecx)
420 movl %ebx,PCB_EBX(%ecx)
421 movl %esp,PCB_ESP(%ecx)
422 movl %ebp,PCB_EBP(%ecx)
423 movl %esi,PCB_ESI(%ecx)
424 movl %edi,PCB_EDI(%ecx)
425 movl %gs,PCB_GS(%ecx)
429 * If npxthread == NULL, then the npx h/w state is irrelevant and the
430 * state had better already be in the pcb. This is true for forks
431 * but not for dumps (the old book-keeping with FP flags in the pcb
432 * always lost for dumps because the dump pcb has 0 flags).
434 * If npxthread != NULL, then we have to save the npx h/w state to
435 * npxthread's pcb and copy it to the requested pcb, or save to the
436 * requested pcb and reload. Copying is easier because we would
437 * have to handle h/w bugs for reloading. We used to lose the
438 * parent's npx state for forks by forgetting to reload.
440 movl PCPU(npxthread),%eax
445 movl TD_PCB(%eax),%eax
446 leal PCB_SAVEFPU(%eax),%eax
454 pushl $PCB_SAVEFPU_SIZE
455 leal PCB_SAVEFPU(%ecx),%ecx
460 #endif /* NNPX > 0 */
466 * cpu_idle_restore() (current thread in %eax on entry) (one-time execution)
468 * Don't bother setting up any regs other then %ebp so backtraces
469 * don't die. This restore function is used to bootstrap into the
470 * cpu_idle() LWKT only, after that cpu_lwkt_*() will be used for
473 * Clear TDF_RUNNING in old thread only after we've cleaned up %cr3.
475 * If we are an AP we have to call ap_init() before jumping to
476 * cpu_idle(). ap_init() will synchronize with the BP and finish
477 * setting up various ncpu-dependant globaldata fields. This may
478 * happen on UP as well as SMP if we happen to be simulating multiple
481 ENTRY(cpu_idle_restore)
487 andl $~TDF_RUNNING,TD_FLAGS(%ebx)
488 orl $TDF_RUNNING,TD_FLAGS(%eax)
499 * cpu_kthread_restore() (current thread is %eax on entry) (one-time execution)
501 * Don't bother setting up any regs other then %ebp so backtraces
502 * don't die. This restore function is used to bootstrap into an
503 * LWKT based kernel thread only. cpu_lwkt_switch() will be used
506 * Since all of our context is on the stack we are reentrant and
507 * we can release our critical section and enable interrupts early.
509 ENTRY(cpu_kthread_restore)
512 movl TD_PCB(%eax),%edx
515 andl $~TDF_RUNNING,TD_FLAGS(%ebx)
516 orl $TDF_RUNNING,TD_FLAGS(%eax)
517 subl $TDPRI_CRIT,TD_PRI(%eax)
518 popl %eax /* kthread exit function */
519 pushl PCB_EBX(%edx) /* argument to ESI function */
520 pushl %eax /* set exit func as return address */
521 movl PCB_ESI(%edx),%eax
527 * Standard LWKT switching function. Only non-scratch registers are
528 * saved and we don't bother with the MMU state or anything else.
530 * This function is always called while in a critical section.
532 * There is a one-instruction window where curthread is the new
533 * thread but %esp still points to the old thread's stack, but
534 * we are protected by a critical section so it is ok.
538 ENTRY(cpu_lwkt_switch)
545 movl PCPU(curthread),%ebx
546 pushl $cpu_lwkt_restore
547 movl %esp,TD_SP(%ebx)
548 movl %eax,PCPU(curthread)
549 movl TD_SP(%eax),%esp
552 * eax contains new thread, ebx contains old thread.
557 * cpu_lwkt_restore() (current thread in %eax on entry)
559 * Standard LWKT restore function. This function is always called
560 * while in a critical section.
562 * Warning: due to preemption the restore function can be used to
563 * 'return' to the original thread. Interrupt disablement must be
564 * protected through the switch so we cannot run splz here.
566 * YYY we theoretically do not need to load IdlePTD into cr3, but if
567 * so we need a way to detect when the PTD we are using is being
568 * deleted due to a process exiting.
570 ENTRY(cpu_lwkt_restore)
571 movl IdlePTD,%ecx /* YYY borrow but beware desched/cpuchg/exit */
577 andl $~TDF_RUNNING,TD_FLAGS(%ebx)
578 orl $TDF_RUNNING,TD_FLAGS(%eax)