task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
__switch_to_xtra(prev_p, next_p, tss);
- /* 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
- *
- * tsk_used_math() checks prevent calling math_state_restore(),
- * which can sleep in the case of !tsk_used_math()
+ /*
+ * Preload the FPU context, now that we've determined that the
+ * task is likely to be using it.
*/
- if (tsk_used_math(next_p) && next_p->fpu_counter > 5)
- math_state_restore();
+ if (preload_fpu)
+ __math_state_restore();
+ /*
+ * There's a problem with moving the arch_install_thread_hw_breakpoint()
+ * call before current is updated. Suppose a kernel breakpoint is
+ * triggered in between the two, the hw-breakpoint handler will see that
+ * the 'current' task does not have TIF_DEBUG flag set and will think it
+ * is leftover from an old task (lazy switching) and will erase it. Then
+ * until the next context switch, no user-breakpoints will be installed.
+ *
+ * The real problem is that it's impossible to update both current and
+ * physical debug registers at the same instant, so there will always be
+ * a window in which they disagree and a breakpoint might get triggered.
+ * Since we use lazy switching, we are forced to assume that a
+ * disagreement means that current is correct and the exception is due
+ * to lazy debug register switching.
+ */
+ if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG)))
+ arch_install_thread_hw_breakpoint(next_p);
+
return prev_p;
}
set_debugreg(vcpu->arch.eff_db[3], 3);
}
- KVMTRACE_0D(VMENTRY, vcpu, entryexit);
+ trace_kvm_entry(vcpu->vcpu_id);
kvm_x86_ops->run(vcpu, kvm_run);
- if (unlikely(vcpu->arch.switch_db_regs)) {
- set_debugreg(0, 7);
- set_debugreg(vcpu->arch.host_db[0], 0);
- set_debugreg(vcpu->arch.host_db[1], 1);
- set_debugreg(vcpu->arch.host_db[2], 2);
- set_debugreg(vcpu->arch.host_db[3], 3);
+ if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) {
- set_debugreg(current->thread.debugreg0, 0);
- set_debugreg(current->thread.debugreg1, 1);
- set_debugreg(current->thread.debugreg2, 2);
- set_debugreg(current->thread.debugreg3, 3);
++ set_debugreg(current->thread.debugreg[0], 0);
++ set_debugreg(current->thread.debugreg[1], 1);
++ set_debugreg(current->thread.debugreg[2], 2);
++ set_debugreg(current->thread.debugreg[3], 3);
+ set_debugreg(current->thread.debugreg6, 6);
+ set_debugreg(current->thread.debugreg7, 7);
}
- set_debugreg(vcpu->arch.host_dr6, 6);
- set_debugreg(vcpu->arch.host_dr7, 7);
set_bit(KVM_REQ_KICK, &vcpu->requests);
local_irq_enable();