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>

5 files changed, 57 insertions, 10 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) {
diff --git a/src/cpu/kvm/base.hh b/src/cpu/kvm/base.hh
index 4aeed2286..dd27328be 100644
--- a/src/cpu/kvm/base.hh
+++ b/src/cpu/kvm/base.hh
@@ -89,6 +89,7 @@ class BaseKvmCPU : public BaseCPU
 
     DrainState drain() override;
     void drainResume() override;
+    void notifyFork() override;
 
     void switchOut() override;
     void takeOverFrom(BaseCPU *cpu) override;
diff --git a/src/cpu/kvm/vm.cc b/src/cpu/kvm/vm.cc
index 87a76c242..ccf739305 100644
--- a/src/cpu/kvm/vm.cc
+++ b/src/cpu/kvm/vm.cc
@@ -291,12 +291,12 @@ Kvm::createVM()
 
 KvmVM::KvmVM(KvmVMParams *params)
     : SimObject(params),
-      kvm(), system(params->system),
-      vmFD(kvm.createVM()),
+      kvm(new Kvm()), system(params->system),
+      vmFD(kvm->createVM()),
       started(false),
       nextVCPUID(0)
 {
-    maxMemorySlot = kvm.capNumMemSlots();
+    maxMemorySlot = kvm->capNumMemSlots();
     /* If we couldn't determine how memory slots there are, guess 32. */
     if (!maxMemorySlot)
         maxMemorySlot = 32;
@@ -307,7 +307,25 @@ KvmVM::KvmVM(KvmVMParams *params)
 
 KvmVM::~KvmVM()
 {
-    close(vmFD);
+    if (vmFD != -1)
+        close(vmFD);
+
+    if (kvm)
+        delete kvm;
+}
+
+void
+KvmVM::notifyFork()
+{
+    if (vmFD != -1) {
+        if (close(vmFD) == -1)
+            warn("kvm VM: notifyFork failed to close vmFD\n");
+
+        vmFD = -1;
+
+        delete kvm;
+        kvm = NULL;
+    }
 }
 
 void
diff --git a/src/cpu/kvm/vm.hh b/src/cpu/kvm/vm.hh
index 8f834a06e..560efb606 100644
--- a/src/cpu/kvm/vm.hh
+++ b/src/cpu/kvm/vm.hh
@@ -295,6 +295,8 @@ class KvmVM : public SimObject
     KvmVM(KvmVMParams *params);
     virtual ~KvmVM();
 
+    void notifyFork();
+
     /**
      * Setup a shared three-page memory region used by the internals
      * of KVM. This is currently only needed by x86 implementations.
@@ -396,7 +398,7 @@ class KvmVM : public SimObject
     int createDevice(uint32_t type, uint32_t flags = 0);
 
     /** Global KVM interface */
-    Kvm kvm;
+    Kvm *kvm;
 
 #if defined(__aarch64__)
   public: // ARM-specific
@@ -504,7 +506,7 @@ class KvmVM : public SimObject
     System *system;
 
     /** KVM VM file descriptor */
-    const int vmFD;
+    int vmFD;
 
     /** Has delayedStartup() already been called? */
     bool started;
diff --git a/src/cpu/kvm/x86_cpu.cc b/src/cpu/kvm/x86_cpu.cc
index f3e5edaed..c6c874dc4 100644
--- a/src/cpu/kvm/x86_cpu.cc
+++ b/src/cpu/kvm/x86_cpu.cc
@@ -519,7 +519,7 @@ X86KvmCPU::X86KvmCPU(X86KvmCPUParams *params)
     : BaseKvmCPU(params),
       useXSave(params->useXSave)
 {
-    Kvm &kvm(vm.kvm);
+    Kvm &kvm(*vm.kvm);
 
     if (!kvm.capSetTSSAddress())
         panic("KVM: Missing capability (KVM_CAP_SET_TSS_ADDR)\n");
@@ -649,7 +649,7 @@ X86KvmCPU::dumpVCpuEvents() const
 void
 X86KvmCPU::dumpMSRs() const
 {
-    const Kvm::MSRIndexVector &supported_msrs(vm.kvm.getSupportedMSRs());
+    const Kvm::MSRIndexVector &supported_msrs(vm.kvm->getSupportedMSRs());
     std::unique_ptr<struct kvm_msrs> msrs(
         newVarStruct<struct kvm_msrs, struct kvm_msr_entry>(
             supported_msrs.size()));
@@ -1539,7 +1539,7 @@ const Kvm::MSRIndexVector &
 X86KvmCPU::getMsrIntersection() const
 {
     if (cachedMsrIntersection.empty()) {
-        const Kvm::MSRIndexVector &kvm_msrs(vm.kvm.getSupportedMSRs());
+        const Kvm::MSRIndexVector &kvm_msrs(vm.kvm->getSupportedMSRs());
 
         DPRINTF(Kvm, "kvm-x86: Updating MSR intersection\n");
         for (auto it = kvm_msrs.cbegin(); it != kvm_msrs.cend(); ++it) {