kvm: Shutdown KVM and disconnect performance counters on fork

We can't/shouldn't use KVM after a fork since the child and parent
probably point to the same VM. Knowing the exact effects of this is
hard, but they are likely to be messy. We also disconnect the
performance counters attached to the guest. This works around what
seems to be a kernel bug where spurious SIGIOs get delivered to the
forked child process.

Signed-off-by: Andreas Sandberg <andreas@sandberg.pp.se>
[sascha.bischoff@arm.com: Rebased patches onto a newer gem5 version]
Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
[andreas.sandberg@arm.com: Fatal if entering KVM in child process ]
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>

1 files changed, 27 insertions, 1 deletions

diff --git a/src/cpu/kvm/base.cc b/src/cpu/kvm/base.cc
index 32f94eca8..ea0f494e3 100644
--- a/src/cpu/kvm/base.cc
+++ b/src/cpu/kvm/base.cc
@@ -125,7 +125,7 @@ BaseKvmCPU::startup()
     const BaseKvmCPUParams * const p(
         dynamic_cast<const BaseKvmCPUParams *>(params()));
 
-    Kvm &kvm(vm.kvm);
+    Kvm &kvm(*vm.kvm);
 
     BaseCPU::startup();
 
@@ -363,6 +363,29 @@ BaseKvmCPU::drainResume()
 }
 
 void
+BaseKvmCPU::notifyFork()
+{
+    // We should have drained prior to forking, which means that the
+    // tick event shouldn't be scheduled and the CPU is idle.
+    assert(!tickEvent.scheduled());
+    assert(_status == Idle);
+
+    if (vcpuFD != -1) {
+        if (close(vcpuFD) == -1)
+            warn("kvm CPU: notifyFork failed to close vcpuFD\n");
+
+        if (_kvmRun)
+            munmap(_kvmRun, vcpuMMapSize);
+
+        vcpuFD = -1;
+        _kvmRun = NULL;
+
+        hwInstructions.detach();
+        hwCycles.detach();
+    }
+}
+
+void
 BaseKvmCPU::switchOut()
 {
     DPRINTF(Kvm, "switchOut\n");
@@ -617,6 +640,9 @@ Tick
 BaseKvmCPU::kvmRun(Tick ticks)
 {
     Tick ticksExecuted;
+    fatal_if(vcpuFD == -1,
+             "Trying to run a KVM CPU in a forked child process. "
+             "This is not supported.\n");
     DPRINTF(KvmRun, "KVM: Executing for %i ticks\n", ticks);
 
     if (ticks == 0) {