void release_thread(struct task_struct *dead_task)
{
if (dead_task->mm) {
- if (dead_task->mm->context.size) {
+ if (dead_task->mm->context.ldt) {
printk("WARNING: dead process %8s still has LDT? <%p/%d>\n",
dead_task->comm,
- dead_task->mm->context.ldt,
- dead_task->mm->context.size);
+ dead_task->mm->context.ldt->entries,
+ dead_task->mm->context.ldt->size);
BUG();
}
}
int cpu = smp_processor_id();
struct tss_struct *tss = &per_cpu(init_tss, cpu);
unsigned fsindex, gsindex;
- bool preload_fpu;
+ fpu_switch_t fpu;
- /*
- * If the task has used fpu the last 5 timeslices, just do a full
- * restore of the math state immediately to avoid the trap; the
- * chances of needing FPU soon are obviously high now
- */
- preload_fpu = tsk_used_math(next_p) && next_p->fpu_counter > 5;
+ fpu = switch_fpu_prepare(prev_p, next_p);
- /* we're going to use this soon, after a few expensive things */
- if (preload_fpu)
- prefetch(next->fpu.state);
-
- /*
- * Reload esp0, LDT and the page table pointer:
- */
+ /* Reload esp0 and ss1. */
load_sp0(tss, next);
- /*
- * Switch DS and ES.
- * This won't pick up thread selector changes, but I guess that is ok.
- */
- savesegment(es, prev->es);
- if (unlikely(next->es | prev->es))
- loadsegment(es, next->es);
-
- savesegment(ds, prev->ds);
- if (unlikely(next->ds | prev->ds))
- loadsegment(ds, next->ds);
-
-
/* We must save %fs and %gs before load_TLS() because
* %fs and %gs may be cleared by load_TLS().
*
savesegment(fs, fsindex);
savesegment(gs, gsindex);
+ /*
+ * Load TLS before restoring any segments so that segment loads
+ * reference the correct GDT entries.
+ */
load_TLS(next, cpu);
- /* Must be after DS reload */
- __unlazy_fpu(prev_p);
-
- /* Make sure cpu is ready for new context */
- if (preload_fpu)
- clts();
-
/*
- * Leave lazy mode, flushing any hypercalls made here.
- * This must be done before restoring TLS segments so
- * the GDT and LDT are properly updated, and must be
- * done before math_state_restore, so the TS bit is up
- * to date.
+ * Leave lazy mode, flushing any hypercalls made here. This
+ * must be done after loading TLS entries in the GDT but before
+ * loading segments that might reference them, and and it must
+ * be done before math_state_restore, so the TS bit is up to
+ * date.
*/
arch_end_context_switch(next_p);
+ /* Switch DS and ES.
+ *
+ * Reading them only returns the selectors, but writing them (if
+ * nonzero) loads the full descriptor from the GDT or LDT. The
+ * LDT for next is loaded in switch_mm, and the GDT is loaded
+ * above.
+ *
+ * We therefore need to write new values to the segment
+ * registers on every context switch unless both the new and old
+ * values are zero.
+ *
+ * Note that we don't need to do anything for CS and SS, as
+ * those are saved and restored as part of pt_regs.
+ */
+ savesegment(es, prev->es);
+ if (unlikely(next->es | prev->es))
+ loadsegment(es, next->es);
+
+ savesegment(ds, prev->ds);
+ if (unlikely(next->ds | prev->ds))
+ loadsegment(ds, next->ds);
+
/*
* Switch FS and GS.
*
- * Segment register != 0 always requires a reload. Also
- * reload when it has changed. When prev process used 64bit
- * base always reload to avoid an information leak.
+ * These are even more complicated than FS and GS: they have
+ * 64-bit bases are that controlled by arch_prctl. Those bases
+ * only differ from the values in the GDT or LDT if the selector
+ * is 0.
+ *
+ * Loading the segment register resets the hidden base part of
+ * the register to 0 or the value from the GDT / LDT. If the
+ * next base address zero, writing 0 to the segment register is
+ * much faster than using wrmsr to explicitly zero the base.
+ *
+ * The thread_struct.fs and thread_struct.gs values are 0
+ * if the fs and gs bases respectively are not overridden
+ * from the values implied by fsindex and gsindex. They
+ * are nonzero, and store the nonzero base addresses, if
+ * the bases are overridden.
+ *
+ * (fs != 0 && fsindex != 0) || (gs != 0 && gsindex != 0) should
+ * be impossible.
+ *
+ * Therefore we need to reload the segment registers if either
+ * the old or new selector is nonzero, and we need to override
+ * the base address if next thread expects it to be overridden.
+ *
+ * This code is unnecessarily slow in the case where the old and
+ * new indexes are zero and the new base is nonzero -- it will
+ * unnecessarily write 0 to the selector before writing the new
+ * base address.
+ *
+ * Note: This all depends on arch_prctl being the only way that
+ * user code can override the segment base. Once wrfsbase and
+ * wrgsbase are enabled, most of this code will need to change.
*/
if (unlikely(fsindex | next->fsindex | prev->fs)) {
loadsegment(fs, next->fsindex);
+
/*
- * Check if the user used a selector != 0; if yes
- * clear 64bit base, since overloaded base is always
- * mapped to the Null selector
+ * If user code wrote a nonzero value to FS, then it also
+ * cleared the overridden base address.
+ *
+ * XXX: if user code wrote 0 to FS and cleared the base
+ * address itself, we won't notice and we'll incorrectly
+ * restore the prior base address next time we reschdule
+ * the process.
*/
if (fsindex)
prev->fs = 0;
}
- /* when next process has a 64bit base use it */
if (next->fs)
wrmsrl(MSR_FS_BASE, next->fs);
prev->fsindex = fsindex;
if (unlikely(gsindex | next->gsindex | prev->gs)) {
load_gs_index(next->gsindex);
+
+ /* This works (and fails) the same way as fsindex above. */
if (gsindex)
prev->gs = 0;
}
wrmsrl(MSR_KERNEL_GS_BASE, next->gs);
prev->gsindex = gsindex;
+ switch_fpu_finish(next_p, fpu);
+
/*
* Switch the PDA and FPU contexts.
*/
task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
__switch_to_xtra(prev_p, next_p, tss);
- /*
- * Preload the FPU context, now that we've determined that the
- * task is likely to be using it.
- */
- if (preload_fpu)
- __math_state_restore();
-
return prev_p;
}
current_thread_info()->status |= TS_COMPAT;
}
+/*
+ * Called from fs/proc with a reference on @p to find the function
+ * which called into schedule(). This needs to be done carefully
+ * because the task might wake up and we might look at a stack
+ * changing under us.
+ */
unsigned long get_wchan(struct task_struct *p)
{
- unsigned long stack;
- u64 fp, ip;
+ unsigned long start, bottom, top, sp, fp, ip;
int count = 0;
if (!p || p == current || p->state == TASK_RUNNING)
return 0;
- stack = (unsigned long)task_stack_page(p);
- if (p->thread.sp < stack || p->thread.sp >= stack+THREAD_SIZE)
+
+ start = (unsigned long)task_stack_page(p);
+ if (!start)
+ return 0;
+
+ /*
+ * Layout of the stack page:
+ *
+ * ----------- topmax = start + THREAD_SIZE - sizeof(unsigned long)
+ * PADDING
+ * ----------- top = topmax - TOP_OF_KERNEL_STACK_PADDING
+ * stack
+ * ----------- bottom = start + sizeof(thread_info)
+ * thread_info
+ * ----------- start
+ *
+ * The tasks stack pointer points at the location where the
+ * framepointer is stored. The data on the stack is:
+ * ... IP FP ... IP FP
+ *
+ * We need to read FP and IP, so we need to adjust the upper
+ * bound by another unsigned long.
+ */
+ top = start + THREAD_SIZE;
+ top -= 2 * sizeof(unsigned long);
+ bottom = start + sizeof(struct thread_info);
+
+ sp = ACCESS_ONCE(p->thread.sp);
+ if (sp < bottom || sp > top)
return 0;
- fp = *(u64 *)(p->thread.sp);
+
+ fp = ACCESS_ONCE(*(unsigned long *)sp);
do {
- if (fp < (unsigned long)stack ||
- fp >= (unsigned long)stack+THREAD_SIZE)
+ if (fp < bottom || fp > top)
return 0;
- ip = *(u64 *)(fp+8);
+ ip = ACCESS_ONCE(*(unsigned long *)(fp + sizeof(unsigned long)));
if (!in_sched_functions(ip))
return ip;
- fp = *(u64 *)fp;
- } while (count++ < 16);
+ fp = ACCESS_ONCE(*(unsigned long *)fp);
+ } while (count++ < 16 && p->state != TASK_RUNNING);
return 0;
}
git.openpandora.org / pandora-kernel.git / blobdiff