2 * Copyright (c) 2003,2004,2008 The DragonFly Project. All rights reserved.
3 * Copyright (c) 2008 Jordan Gordeev.
5 * This code is derived from software contributed to The DragonFly Project
6 * by Matthew Dillon <dillon@backplane.com>
8 * Redistribution and use in source and binary forms, with or without
9 * 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
16 * the documentation and/or other materials provided with the
18 * 3. Neither the name of The DragonFly Project nor the names of its
19 * contributors may be used to endorse or promote products derived
20 * from this software without specific, prior written permission.
22 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
23 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
24 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
25 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
26 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
27 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
28 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
29 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
30 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
31 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
32 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * Copyright (c) 1990 The Regents of the University of California.
36 * All rights reserved.
38 * This code is derived from software contributed to Berkeley by
41 * Redistribution and use in source and binary forms, with or without
42 * modification, are permitted provided that the following conditions
44 * 1. Redistributions of source code must retain the above copyright
45 * notice, this list of conditions and the following disclaimer.
46 * 2. Redistributions in binary form must reproduce the above copyright
47 * notice, this list of conditions and the following disclaimer in the
48 * documentation and/or other materials provided with the distribution.
49 * 3. Neither the name of the University nor the names of its contributors
50 * may be used to endorse or promote products derived from this software
51 * without specific prior written permission.
53 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
54 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
55 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
56 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
57 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
58 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
59 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
60 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
61 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
62 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
65 * $FreeBSD: src/sys/i386/i386/swtch.s,v 1.89.2.10 2003/01/23 03:36:24 ps Exp $
68 //#include "use_npx.h"
70 #include <sys/rtprio.h>
72 #include <machine/asmacros.h>
73 #include <machine/segments.h>
75 #include <machine/pmap.h>
77 #include <machine_base/apic/apicreg.h>
79 #include <machine/lock.h>
83 #define MPLOCKED lock ;
88 * This feature allows the preempting (interrupt) kernel thread to borrow
89 * %cr3 from the user process it interrupts, allowing us to do-away with
90 * two %cr3 stores, two atomic ops (pm_active is not modified), and pmap
91 * lock tests (not needed since pm_active is not modified).
93 * Unfortunately, I couldn't really measure any result so for now the
94 * optimization is disabled.
96 #undef PREEMPT_OPTIMIZE
101 * This optimization attempted to avoid a %cr3 store and atomic op, and
102 * it might have been useful on older cpus but newer cpus (and more
103 * importantly multi-core cpus) generally do not switch between LWPs on
104 * the same cpu. Multiple user threads are more likely to be distributed
105 * across multiple cpus. In cpu-bound situations the scheduler will already
106 * be in batch-mode (meaning relatively few context-switches/sec), and
107 * otherwise the lwp(s) are likely to be blocked waiting for events.
109 * On the flip side, the conditionals this option uses measurably reduce
110 * performance (just slightly, honestly). So this option is disabled.
112 #undef LWP_SWITCH_OPTIMIZE
115 * Global Declarations
120 .globl lwkt_switch_return
122 #if defined(SWTCH_OPTIM_STATS)
123 .globl swtch_optim_stats, tlb_flush_count
124 swtch_optim_stats
: .long 0 /* number of _swtch_optims */
125 tlb_flush_count
: .long 0
134 * cpu_heavy_switch(struct thread *next_thread)
136 * Switch from the current thread to a new thread. This entry
137 * is normally called via the thread->td_switch function, and will
138 * only be called when the current thread is a heavy weight process.
140 * Some instructions have been reordered to reduce pipeline stalls.
142 * YYY disable interrupts once giant is removed.
144 ENTRY
(cpu_heavy_switch
)
146 * Save RIP, RSP and callee-saved registers (RBX, RBP, R12-R15).
148 movq PCPU
(curthread
),%rcx
149 /* On top of the stack is the return adress. */
150 movq
(%rsp
),%rax
/* (reorder optimization) */
151 movq TD_PCB
(%rcx
),%rdx
/* RDX = PCB */
152 movq
%rax
,PCB_RIP
(%rdx
) /* return PC may be modified */
153 movq
%rbx
,PCB_RBX
(%rdx
)
154 movq
%rsp
,PCB_RSP
(%rdx
)
155 movq
%rbp
,PCB_RBP
(%rdx
)
156 movq
%r12,PCB_R12
(%rdx
)
157 movq
%r13,PCB_R13
(%rdx
)
158 movq
%r14,PCB_R14
(%rdx
)
159 movq
%r15,PCB_R15
(%rdx
)
162 * Clear the cpu bit in the pmap active mask. The restore
163 * function will set the bit in the pmap active mask.
165 * If we are switching away due to a preempt, TD_PREEMPTED(%rdi)
166 * will be non-NULL. In this situation we do want to avoid extra
167 * atomic ops and %cr3 reloads (see top of file for reasoning).
169 * NOTE: Do not try to optimize avoiding the %cr3 reload or pm_active
170 * adjustment. This mattered on uni-processor systems but in
171 * multi-core systems we are highly unlikely to be switching
172 * to another thread belonging to the same process on this cpu.
174 * (more likely the target thread is still sleeping, or if cpu-
175 * bound the scheduler is in batch mode and the switch rate is
178 movq
%rcx
,%rbx
/* RBX = oldthread */
179 #ifdef PREEMPT_OPTIMIZE
181 * If we are being preempted the target thread borrows our %cr3
182 * and we leave our pmap bits intact for the duration.
184 movq TD_PREEMPTED
(%rdi
),%r13
189 movq TD_LWP
(%rcx
),%rcx
/* RCX = oldlwp */
190 movq LWP_VMSPACE
(%rcx
), %rcx
/* RCX = oldvmspace */
191 #ifdef LWP_SWITCH_OPTIMIZE
192 movq TD_LWP
(%rdi
),%r13 /* R13 = newlwp */
193 testq
%r13,%r13 /* might not be a heavy */
195 cmpq LWP_VMSPACE
(%r13),%rcx
/* same vmspace? */
199 movq PCPU
(cpumask_simple
),%rsi
200 movq PCPU
(cpumask_offset
),%r12
202 MPLOCKED andq
%rsi
, VM_PMAP+PM_ACTIVE
(%rcx
, %r12, 1)
206 * Push the LWKT switch restore function, which resumes a heavy
207 * weight process. Note that the LWKT switcher is based on
208 * TD_SP, while the heavy weight process switcher is based on
209 * PCB_RSP. TD_SP is usually two ints pushed relative to
210 * PCB_RSP. We push the flags for later restore by cpu_heavy_restore.
214 movq $cpu_heavy_restore
, %rax
216 movq
%rsp
,TD_SP
(%rbx
)
219 * Save debug regs if necessary
221 movq PCB_FLAGS
(%rdx
),%rax
222 andq $PCB_DBREGS
,%rax
223 jz
1f
/* no, skip over */
224 movq
%dr7
,%rax
/* yes, do the save */
225 movq
%rax
,PCB_DR7
(%rdx
)
226 /* JG correct value? */
227 andq $
0x0000fc00, %rax
/* disable all watchpoints */
230 movq
%rax
,PCB_DR6
(%rdx
)
232 movq
%rax
,PCB_DR3
(%rdx
)
234 movq
%rax
,PCB_DR2
(%rdx
)
236 movq
%rax
,PCB_DR1
(%rdx
)
238 movq
%rax
,PCB_DR0
(%rdx
)
243 * Save the FP state if we have used the FP. Note that calling
244 * npxsave will NULL out PCPU(npxthread).
246 cmpq
%rbx
,PCPU
(npxthread
)
248 movq
%rdi
,%r12 /* save %rdi. %r12 is callee-saved */
249 movq TD_SAVEFPU
(%rbx
),%rdi
250 call npxsave
/* do it in a big C function */
251 movq
%r12,%rdi
/* restore %rdi */
256 * Switch to the next thread, which was passed as an argument
257 * to cpu_heavy_switch(). The argument is in %rdi.
258 * Set the current thread, load the stack pointer,
259 * and 'ret' into the switch-restore function.
261 * The switch restore function expects the new thread to be in %rax
262 * and the old one to be in %rbx.
264 * There is a one-instruction window where curthread is the new
265 * thread but %rsp still points to the old thread's stack, but
266 * we are protected by a critical section so it is ok.
268 movq
%rdi
,%rax
/* RAX = newtd, RBX = oldtd */
269 movq
%rax
,PCPU
(curthread
)
270 movq TD_SP
(%rax
),%rsp
272 END
(cpu_heavy_switch
)
275 * cpu_exit_switch(struct thread *next)
277 * The switch function is changed to this when a thread is going away
278 * for good. We have to ensure that the MMU state is not cached, and
279 * we don't bother saving the existing thread state before switching.
281 * At this point we are in a critical section and this cpu owns the
282 * thread's token, which serves as an interlock until the switchout is
285 ENTRY
(cpu_exit_switch
)
287 #ifdef PREEMPT_OPTIMIZE
289 * If we were preempting we are switching back to the original thread.
290 * In this situation we already have the original thread's %cr3 and
291 * should not replace it!
293 testl $TDF_PREEMPT_DONE
, TD_FLAGS
(%rdi
)
298 * Get us out of the vmspace
307 movq PCPU
(curthread
),%rbx
310 * If this is a process/lwp, deactivate the pmap after we've
313 movq TD_LWP
(%rbx
),%rcx
316 movq LWP_VMSPACE
(%rcx
), %rcx
/* RCX = vmspace */
318 movq PCPU
(cpumask_simple
),%rax
319 movq PCPU
(cpumask_offset
),%r12
321 MPLOCKED andq
%rax
, VM_PMAP+PM_ACTIVE
(%rcx
, %r12, 1)
324 * Switch to the next thread. RET into the restore function, which
325 * expects the new thread in RAX and the old in RBX.
327 * There is a one-instruction window where curthread is the new
328 * thread but %rsp still points to the old thread's stack, but
329 * we are protected by a critical section so it is ok.
333 movq
%rax
,PCPU
(curthread
)
334 movq TD_SP
(%rax
),%rsp
339 * cpu_heavy_restore() (current thread in %rax on entry, old thread in %rbx)
341 * Restore the thread after an LWKT switch. This entry is normally
342 * called via the LWKT switch restore function, which was pulled
343 * off the thread stack and jumped to.
345 * This entry is only called if the thread was previously saved
346 * using cpu_heavy_switch() (the heavy weight process thread switcher),
347 * or when a new process is initially scheduled.
349 * NOTE: The lwp may be in any state, not necessarily LSRUN, because
350 * a preemption switch may interrupt the process and then return via
353 * YYY theoretically we do not have to restore everything here, a lot
354 * of this junk can wait until we return to usermode. But for now
355 * we restore everything.
357 * YYY the PCB crap is really crap, it makes startup a bitch because
358 * we can't switch away.
360 * YYY note: spl check is done in mi_switch when it splx()'s.
363 ENTRY
(cpu_heavy_restore
)
364 movq TD_PCB
(%rax
),%rdx
/* RDX = PCB */
365 movq
%rdx
, PCPU
(common_tss
) + TSS_RSP0
368 #if defined(SWTCH_OPTIM_STATS)
369 incl _swtch_optim_stats
371 #ifdef PREEMPT_OPTIMIZE
373 * If restoring our thread after a preemption has returned to
374 * us, our %cr3 and pmap were borrowed and are being returned to
375 * us and no further action on those items need be taken.
377 testl $TDF_PREEMPT_DONE
, TD_FLAGS
(%rax
)
382 * Tell the pmap that our cpu is using the VMSPACE now. We cannot
383 * safely test/reload %cr3 until after we have set the bit in the
386 * We must do an interlocked test of the CPULOCK_EXCL at the same
387 * time. If found to be set we will have to wait for it to clear
388 * and then do a forced reload of %cr3 (even if the value matches).
390 * XXX When switching between two LWPs sharing the same vmspace
391 * the cpu_heavy_switch() code currently avoids clearing the
392 * cpu bit in PM_ACTIVE. So if the bit is already set we can
393 * avoid checking for the interlock via CPULOCK_EXCL. We currently
394 * do not perform this optimization.
396 movq TD_LWP
(%rax
),%rcx
397 movq LWP_VMSPACE
(%rcx
),%rcx
/* RCX = vmspace */
399 movq PCPU
(cpumask_simple
),%rsi
400 movq PCPU
(cpumask_offset
),%r12
401 MPLOCKED orq
%rsi
, VM_PMAP+PM_ACTIVE
(%rcx
, %r12, 1)
403 movl VM_PMAP+PM_ACTIVE_LOCK
(%rcx
),%esi
404 testl $CPULOCK_EXCL
,%esi
407 movq
%rax
,%r12 /* save newthread ptr */
408 movq
%rcx
,%rdi
/* (found to be set) */
409 call pmap_interlock_wait
/* pmap_interlock_wait(%rdi:vm) */
413 * Need unconditional load cr3
415 movq TD_PCB
(%rax
),%rdx
/* RDX = PCB */
416 movq PCB_CR3
(%rdx
),%rcx
/* RCX = desired CR3 */
417 jmp
2f
/* unconditional reload */
420 * Restore the MMU address space. If it is the same as the last
421 * thread we don't have to invalidate the tlb (i.e. reload cr3).
423 * XXX Temporary cludge, do NOT do this optimization! The problem
424 * is that the pm_active bit for the cpu had dropped for a small
425 * period of time, just a few cycles, but even one cycle is long
426 * enough for some other cpu doing a pmap invalidation to not see
429 * When that happens, and we don't invltlb (by loading %cr3), we
430 * wind up with a stale TLB.
432 movq TD_PCB
(%rax
),%rdx
/* RDX = PCB */
433 movq
%cr3
,%rsi
/* RSI = current CR3 */
434 movq PCB_CR3
(%rdx
),%rcx
/* RCX = desired CR3 */
438 #if defined(SWTCH_OPTIM_STATS)
439 decl _swtch_optim_stats
440 incl _tlb_flush_count
446 * NOTE: %rbx is the previous thread and %rax is the new thread.
447 * %rbx is retained throughout so we can return it.
449 * lwkt_switch[_return] is responsible for handling TDF_RUNNING.
453 * Deal with the PCB extension, restore the private tss
455 movq PCB_EXT
(%rdx
),%rdi
/* check for a PCB extension */
456 movq $
1,%rcx
/* maybe mark use of a private tss */
463 * Going back to the common_tss. We may need to update TSS_RSP0
464 * which sets the top of the supervisor stack when entering from
465 * usermode. The PCB is at the top of the stack but we need another
466 * 16 bytes to take vm86 into account.
469 /*leaq -TF_SIZE(%rdx),%rcx*/
470 movq
%rcx
, PCPU
(common_tss
) + TSS_RSP0
473 cmpl $
0,PCPU
(private_tss
) /* don't have to reload if */
474 je
3f
/* already using the common TSS */
477 subq
%rcx
,%rcx
/* unmark use of private tss */
480 * Get the address of the common TSS descriptor for the ltr.
481 * There is no way to get the address of a segment-accessed variable
482 * so we store a self-referential pointer at the base of the per-cpu
483 * data area and add the appropriate offset.
486 movq $gd_common_tssd
, %rdi
487 /* JG name for "%gs:0"? */
491 * Move the correct TSS descriptor into the GDT slot, then reload
496 movl
%rcx
,PCPU
(private_tss
) /* mark/unmark private tss */
497 movq PCPU
(tss_gdt
), %rbx
/* entry in GDT */
500 movl $GPROC0_SEL
*8, %esi
/* GSEL(entry, SEL_KPL) */
506 * Restore the user %gs and %fs
508 movq PCB_FSBASE
(%rdx
),%r9
509 cmpq PCPU
(user_fs
),%r9
512 movq
%r9,PCPU
(user_fs
)
513 movl $MSR_FSBASE
,%ecx
514 movl PCB_FSBASE
(%r10),%eax
515 movl PCB_FSBASE+
4(%r10),%edx
519 movq PCB_GSBASE
(%rdx
),%r9
520 cmpq PCPU
(user_gs
),%r9
523 movq
%r9,PCPU
(user_gs
)
524 movl $MSR_KGSBASE
,%ecx
/* later swapgs moves it to GSBASE */
525 movl PCB_GSBASE
(%r10),%eax
526 movl PCB_GSBASE+
4(%r10),%edx
532 * Restore general registers. %rbx is restored later.
534 movq PCB_RSP
(%rdx
), %rsp
535 movq PCB_RBP
(%rdx
), %rbp
536 movq PCB_R12
(%rdx
), %r12
537 movq PCB_R13
(%rdx
), %r13
538 movq PCB_R14
(%rdx
), %r14
539 movq PCB_R15
(%rdx
), %r15
540 movq PCB_RIP
(%rdx
), %rax
547 * Restore the user LDT if we have one
549 cmpl $
0, PCB_USERLDT
(%edx
)
551 movl _default_ldt
,%eax
552 cmpl PCPU
(currentldt
),%eax
555 movl
%eax
,PCPU
(currentldt
)
564 * Restore the user TLS if we have one
572 * Restore the DEBUG register state if necessary.
574 movq PCB_FLAGS
(%rdx
),%rax
575 andq $PCB_DBREGS
,%rax
576 jz
1f
/* no, skip over */
577 movq PCB_DR6
(%rdx
),%rax
/* yes, do the restore */
579 movq PCB_DR3
(%rdx
),%rax
581 movq PCB_DR2
(%rdx
),%rax
583 movq PCB_DR1
(%rdx
),%rax
585 movq PCB_DR0
(%rdx
),%rax
587 movq
%dr7
,%rax
/* load dr7 so as not to disturb */
588 /* JG correct value? */
589 andq $
0x0000fc00,%rax
/* reserved bits */
590 /* JG we've got more registers on x86_64 */
591 movq PCB_DR7
(%rdx
),%rcx
592 /* JG correct value? */
593 andq $~
0x0000fc00,%rcx
598 * Clear the QUICKRET flag when restoring a user process context
599 * so we don't try to do a quick syscall return.
602 andl $~RQF_QUICKRET
,PCPU
(reqflags
)
604 movq PCB_RBX
(%rdx
),%rbx
606 END
(cpu_heavy_restore
)
609 * savectx(struct pcb *pcb)
611 * Update pcb, saving current processor state.
615 /* JG use %rdi instead of %rcx everywhere? */
618 /* caller's return address - child won't execute this routine */
620 movq
%rax
,PCB_RIP
(%rcx
)
623 movq
%rax
,PCB_CR3
(%rcx
)
625 movq
%rbx
,PCB_RBX
(%rcx
)
626 movq
%rsp
,PCB_RSP
(%rcx
)
627 movq
%rbp
,PCB_RBP
(%rcx
)
628 movq
%r12,PCB_R12
(%rcx
)
629 movq
%r13,PCB_R13
(%rcx
)
630 movq
%r14,PCB_R14
(%rcx
)
631 movq
%r15,PCB_R15
(%rcx
)
635 * If npxthread == NULL, then the npx h/w state is irrelevant and the
636 * state had better already be in the pcb. This is true for forks
637 * but not for dumps (the old book-keeping with FP flags in the pcb
638 * always lost for dumps because the dump pcb has 0 flags).
640 * If npxthread != NULL, then we have to save the npx h/w state to
641 * npxthread's pcb and copy it to the requested pcb, or save to the
642 * requested pcb and reload. Copying is easier because we would
643 * have to handle h/w bugs for reloading. We used to lose the
644 * parent's npx state for forks by forgetting to reload.
646 movq PCPU
(npxthread
),%rax
650 pushq
%rcx
/* target pcb */
651 movq TD_SAVEFPU
(%rax
),%rax
/* originating savefpu area */
660 movq $PCB_SAVEFPU_SIZE
,%rdx
661 leaq PCB_SAVEFPU
(%rcx
),%rcx
672 * cpu_idle_restore() (current thread in %rax on entry, old thread in %rbx)
675 * Don't bother setting up any regs other than %rbp so backtraces
676 * don't die. This restore function is used to bootstrap into the
677 * cpu_idle() LWKT only, after that cpu_lwkt_*() will be used for
680 * Clear TDF_RUNNING in old thread only after we've cleaned up %cr3.
681 * This only occurs during system boot so no special handling is
682 * required for migration.
684 * If we are an AP we have to call ap_init() before jumping to
685 * cpu_idle(). ap_init() will synchronize with the BP and finish
686 * setting up various ncpu-dependant globaldata fields. This may
687 * happen on UP as well as SMP if we happen to be simulating multiple
690 ENTRY
(cpu_idle_restore
)
693 xorq
%rbp
,%rbp
/* dummy frame pointer */
694 pushq $
0 /* dummy return pc */
696 /* NOTE: idle thread can never preempt */
700 andl $~TDF_RUNNING
,TD_FLAGS
(%rbx
)
701 orl $TDF_RUNNING
,TD_FLAGS
(%rax
) /* manual, no switch_return */
704 * ap_init can decide to enable interrupts early, but otherwise, or if
705 * we are UP, do it here.
711 * cpu 0's idle thread entry for the first time must use normal
712 * lwkt_switch_return() semantics or a pending cpu migration on
713 * thread0 will deadlock.
719 call lwkt_switch_return
722 END
(cpu_idle_restore
)
725 * cpu_kthread_restore() (current thread is %rax on entry, previous is %rbx)
726 * (one-time execution)
728 * Don't bother setting up any regs other then %rbp so backtraces
729 * don't die. This restore function is used to bootstrap into an
730 * LWKT based kernel thread only. cpu_lwkt_switch() will be used
733 * Because this switch target does not 'return' to lwkt_switch()
734 * we have to call lwkt_switch_return(otd) to clean up otd.
737 * Since all of our context is on the stack we are reentrant and
738 * we can release our critical section and enable interrupts early.
740 ENTRY
(cpu_kthread_restore
)
743 movq TD_PCB
(%rax
),%r13
746 #ifdef PREEMPT_OPTIMIZE
748 * If we are preempting someone we borrow their %cr3, do not overwrite
751 movq TD_PREEMPTED
(%rax
),%r14
759 * rax and rbx come from the switchout code. Call
760 * lwkt_switch_return(otd).
762 * NOTE: unlike i386, %rsi and %rdi are not call-saved regs.
766 call lwkt_switch_return
768 decl TD_CRITCOUNT
(%rax
)
769 movq PCB_R12
(%r13),%rdi
/* argument to RBX function */
770 movq PCB_RBX
(%r13),%rax
/* thread function */
771 /* note: top of stack return address inherited by function */
773 END
(cpu_kthread_restore
)
776 * cpu_lwkt_switch(struct thread *)
778 * Standard LWKT switching function. Only non-scratch registers are
779 * saved and we don't bother with the MMU state or anything else.
781 * This function is always called while in a critical section.
783 * There is a one-instruction window where curthread is the new
784 * thread but %rsp still points to the old thread's stack, but
785 * we are protected by a critical section so it is ok.
787 ENTRY
(cpu_lwkt_switch
)
788 pushq
%rbp
/* JG note: GDB hacked to locate ebp rel to td_sp */
790 movq PCPU
(curthread
),%rbx
/* becomes old thread in restore */
800 * Save the FP state if we have used the FP. Note that calling
801 * npxsave will NULL out PCPU(npxthread).
803 * We have to deal with the FP state for LWKT threads in case they
804 * happen to get preempted or block while doing an optimized
805 * bzero/bcopy/memcpy.
807 cmpq
%rbx
,PCPU
(npxthread
)
809 movq
%rdi
,%r12 /* save %rdi. %r12 is callee-saved */
810 movq TD_SAVEFPU
(%rbx
),%rdi
811 call npxsave
/* do it in a big C function */
812 movq
%r12,%rdi
/* restore %rdi */
816 movq
%rdi
,%rax
/* switch to this thread */
817 pushq $cpu_lwkt_restore
818 movq
%rsp
,TD_SP
(%rbx
)
820 * %rax contains new thread, %rbx contains old thread.
822 movq
%rax
,PCPU
(curthread
)
823 movq TD_SP
(%rax
),%rsp
828 * cpu_lwkt_restore() (current thread in %rax on entry)
830 * Standard LWKT restore function. This function is always called
831 * while in a critical section.
833 * WARNING! Due to preemption the restore function can be used to 'return'
834 * to the original thread. Interrupt disablement must be
835 * protected through the switch so we cannot run splz here.
837 ENTRY
(cpu_lwkt_restore
)
838 #ifdef PREEMPT_OPTIMIZE
840 * If we are preempting someone we borrow their %cr3 and pmap
842 movq TD_PREEMPTED
(%rax
),%r14 /* kernel thread preempting? */
844 jne
1f
/* yes, borrow %cr3 from old thread */
847 * Don't reload %cr3 if it hasn't changed. Since this is a LWKT
848 * thread (a kernel thread), and the kernel_pmap always permanently
849 * sets all pm_active bits, we don't have the same problem with it
850 * that we do with process pmaps.
859 * Safety, clear RSP0 in the tss so it isn't pointing at the
860 * previous thread's kstack (if a heavy weight user thread).
861 * RSP0 should only be used in ring 3 transitions and kernel
862 * threads run in ring 0 so there should be none.
865 movq
%rdx
, PCPU
(common_tss
) + TSS_RSP0
868 * NOTE: %rbx is the previous thread and %rax is the new thread.
869 * %rbx is retained throughout so we can return it.
871 * lwkt_switch[_return] is responsible for handling TDF_RUNNING.
882 END
(cpu_lwkt_restore
)