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Differential D29208 Diff 85604 sys/amd64/amd64/vm_machdep.c

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sys/amd64/amd64/vm_machdep.c

Show First 20 Lines • Show All 158 Lines • ▼ Show 20 Lines if ((flags & RFMEM) == 0) {
pldt->ldt_refcnt > 1 && pldt->ldt_refcnt > 1 &&
user_ldt_alloc(p1, 1) == NULL) user_ldt_alloc(p1, 1) == NULL)
panic("could not copy LDT"); panic("could not copy LDT");
mtx_unlock(&dt_lock); mtx_unlock(&dt_lock);
} }
return; return;
} }
/* Ensure that td1's pcb is up to date. */ /* Ensure that td1's pcb is up to date for user processes. */
if ((td2->td_pflags & TDP_KTHREAD) == 0) {
MPASS(td1 == curthread);
fpuexit(td1); fpuexit(td1);
if (td1 == curthread)
update_pcb_bases(td1->td_pcb); update_pcb_bases(td1->td_pcb);
}
/* Point the stack and pcb to the actual location */ /* Point the stack and pcb to the actual location */
set_top_of_stack_td(td2); set_top_of_stack_td(td2);
td2->td_pcb = pcb2 = get_pcb_td(td2); td2->td_pcb = pcb2 = get_pcb_td(td2);
/* Copy td1's pcb */ /* Copy td1's pcb */
bcopy(td1->td_pcb, pcb2, sizeof(*pcb2)); bcopy(td1->td_pcb, pcb2, sizeof(*pcb2));
/* Properly initialize pcb_save */ /* Properly initialize pcb_save */
pcb2->pcb_save = get_pcb_user_save_pcb(pcb2); pcb2->pcb_save = get_pcb_user_save_pcb(pcb2);
/* Kernel processes start with clean FPU and segment bases. */
if ((td2->td_pflags & TDP_KTHREAD) != 0) {
pcb2->pcb_fsbase = 0;
pcb2->pcb_gsbase = 0;
clear_pcb_flags(pcb2, PCB_FPUINITDONE | PCB_USERFPUINITDONE |
PCB_KERNFPU | PCB_KERNFPU_THR);
kibUnsubmitted
Done
Inline Actions

Should we clear PCB_KERNFPU_THR, or leave it alone?

kib: Should we clear PCB_KERNFPU_THR, or leave it alone?
jhbAuthorUnsubmitted
Done
Inline Actions

To get clean state we should probably clear it as well. That's probably a (small) bug that we don't clear it now.

jhb: To get clean state we should probably clear it as well. That's probably a (small) bug that we…
} else {
MPASS((pcb2->pcb_flags & (PCB_KERNFPU | PCB_KERNFPU_THR)) == 0);
bcopy(get_pcb_user_save_td(td1), get_pcb_user_save_pcb(pcb2), bcopy(get_pcb_user_save_td(td1), get_pcb_user_save_pcb(pcb2),
cpu_max_ext_state_size); cpu_max_ext_state_size);
}
/* Point mdproc and then copy over td1's contents */ /* Point mdproc and then copy over td1's contents */
mdp2 = &p2->p_md; mdp2 = &p2->p_md;
bcopy(&p1->p_md, mdp2, sizeof(*mdp2)); bcopy(&p1->p_md, mdp2, sizeof(*mdp2));
/* /*
* Create a new fresh stack for the new process. * Create a new fresh stack for the new process.
* Copy the trap frame for the return to user mode as if from a * Copy the trap frame for the return to user mode as if from a
▲ Show 20 Lines • Show All 368 Lines • ▼ Show 20 Lines
*/ */
void void
cpu_copy_thread(struct thread *td, struct thread *td0) cpu_copy_thread(struct thread *td, struct thread *td0)
{ {
struct pcb *pcb2; struct pcb *pcb2;
pcb2 = td->td_pcb; pcb2 = td->td_pcb;
/* Ensure that td0's pcb is up to date. */ /* Ensure that td0's pcb is up to date for user threads. */
if ((td->td_pflags & TDP_KTHREAD) == 0) {
MPASS(td0 == curthread);
fpuexit(td0); fpuexit(td0);
if (td0 == curthread)
update_pcb_bases(td0->td_pcb); update_pcb_bases(td0->td_pcb);
}
/* /*
* Copy the upcall pcb. This loads kernel regs. * Copy the upcall pcb. This loads kernel regs.
* Those not loaded individually below get their default * Those not loaded individually below get their default
* values here. * values here.
*/ */
bcopy(td0->td_pcb, pcb2, sizeof(*pcb2)); bcopy(td0->td_pcb, pcb2, sizeof(*pcb2));
clear_pcb_flags(pcb2, PCB_KERNFPU);
pcb2->pcb_save = get_pcb_user_save_pcb(pcb2); pcb2->pcb_save = get_pcb_user_save_pcb(pcb2);
/* Kernel threads start with clean FPU and segment bases. */
if ((td->td_pflags & TDP_KTHREAD) != 0) {
pcb2->pcb_fsbase = 0;
pcb2->pcb_gsbase = 0;
clear_pcb_flags(pcb2, PCB_FPUINITDONE | PCB_USERFPUINITDONE |
PCB_KERNFPU | PCB_KERNFPU_THR);
} else {
MPASS((pcb2->pcb_flags & (PCB_KERNFPU | PCB_KERNFPU_THR)) == 0);
jhbAuthorUnsubmitted
Done
Inline Actions

We could perhaps assert that neither KERNFPU nor KERNFPU_THR is set here instead of clearing. No user process calling thr_new() should have active kernel FPU state here. cpu_fork() doesn't currently bother clearing this flag (so I didn't add it), but I would like these two code blocks to be as identical as possible between cpu_fork() and cpu_copy_thread(). (It's somewhat temping to see if I could come up with some kind of 'copy_pcb' function for the shared logic between the two functions.)

jhb: We could perhaps assert that neither KERNFPU nor KERNFPU_THR is set here instead of clearing.
bcopy(get_pcb_user_save_td(td0), pcb2->pcb_save, bcopy(get_pcb_user_save_td(td0), pcb2->pcb_save,
cpu_max_ext_state_size); cpu_max_ext_state_size);
}
set_pcb_flags_raw(pcb2, PCB_FULL_IRET); set_pcb_flags_raw(pcb2, PCB_FULL_IRET);
/* /*
* Create a new fresh stack for the new thread. * Create a new fresh stack for the new thread.
jhbAuthorUnsubmitted
Done
Inline Actions

This comment seems a bit stale as it doesn't create a stack at all. For exec_setregs where I think this was copied from, we bzero the trap frame before setting registers. I wonder if for the trapframe cpu_thread_copy() shouldn't be more like exec and rely on cpu_set_upcall() instead.

jhb: This comment seems a bit stale as it doesn't create a stack at all. For exec_setregs where I…
jhbAuthorUnsubmitted
Done
Inline Actions

This comment seems a bit stale as it doesn't create a stack at all. For exec_setregs where I think this was copied from, we bzero the trap frame before setting registers. I wonder if for the trapframe cpu_thread_copy() shouldn't be more like exec and rely on cpu_set_upcall() instead.

I tried doing a bzero here and it didn't work out well. cpu_set_upcall() below doesn't set tf_ss (though it sets all the others) which blew up. The 32-bit cpu_set_upcall() doesn't set any seg regs at all, and linux_set_upcall_kse() assumes a copy instead of clear. I will make the comment more accurate though.

jhb: > This comment seems a bit stale as it doesn't create a stack at all. For exec_setregs where I…
*/ */
bcopy(td0->td_frame, td->td_frame, sizeof(struct trapframe)); bcopy(td0->td_frame, td->td_frame, sizeof(struct trapframe));
/* If the current thread has the trap bit set (i.e. a debugger had /* If the current thread has the trap bit set (i.e. a debugger had
* single stepped the process to the system call), we need to clear * single stepped the process to the system call), we need to clear
* the trap flag from the new frame. Otherwise, the new thread will * the trap flag from the new frame. Otherwise, the new thread will
* receive a (likely unexpected) SIGTRAP when it executes the first * receive a (likely unexpected) SIGTRAP when it executes the first
* instruction after returning to userland. * instruction after returning to userland.
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