arm,kvm: update CP15 timer model when exiting Kvm

The ARM MiscRegs implementation has two interfaces: 'normal'
and 'no effect'.  The latter acts as a way to access the
backing store without architectural 'effects'.  For instance,
a normal write to a timer compare value would call into the
timer model to emulate the device.  The 'no effect' interface,
however, would just write the value into the register backing
store and do nothing else.

For Kvm execution, a delicate balance must be struck for the
timer device specifically.  We need the code in the model
to be run, because it contains state other than the register
backing store that must stay in sync.  On the other hand, we
don't necessarily want the timer model to schedule gem5
events when this happens.

In this commit, we ensure that we use the 'effectful'
MiscReg interface when copying the CP15 timer registers
from Kvm back into gem5.  The prior commit makes sure
that this doesn't generate unnecessary timer events
or interrupts.

Change-Id: Id414c2965bd07fc21ac95e3d581ccc9f55cef9f9
Reviewed-on: https://gem5-review.googlesource.com/3543
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

2 files changed, 22 insertions, 6 deletions

diff --git a/src/arch/arm/kvm/armv8_cpu.cc b/src/arch/arm/kvm/armv8_cpu.cc
index 352fb2c80..db2b9c07a 100644
--- a/src/arch/arm/kvm/armv8_cpu.cc
+++ b/src/arch/arm/kvm/armv8_cpu.cc
@@ -114,6 +114,12 @@ const std::vector<ArmV8KvmCPU::MiscRegInfo> ArmV8KvmCPU::miscRegMap = {
     MiscRegInfo(INT_REG(fp_regs.fpcr), MISCREG_FPCR, "FPCR"),
 };
 
+const std::set<MiscRegIndex> ArmV8KvmCPU::deviceRegSet = {
+    MISCREG_CNTV_CTL_EL0,
+    MISCREG_CNTV_CVAL_EL0,
+    MISCREG_CNTKCTL_EL1,
+};
+
 const std::vector<ArmV8KvmCPU::MiscRegInfo> ArmV8KvmCPU::miscRegIdMap = {
     MiscRegInfo(SYS_MPIDR_EL1, MISCREG_MPIDR_EL1, "MPIDR(EL1)"),
 };
@@ -317,7 +323,10 @@ ArmV8KvmCPU::updateThreadContext()
     for (const auto &ri : getSysRegMap()) {
         const auto value(getOneRegU64(ri.kvm));
         DPRINTF(KvmContext, "  %s := 0x%x\n", ri.name, value);
-        tc->setMiscRegNoEffect(ri.idx, value);
+        if (ri.is_device)
+            tc->setMiscReg(ri.idx, value);
+        else
+            tc->setMiscRegNoEffect(ri.idx, value);
     }
 
     PCState pc(getOneRegU64(INT_REG(regs.pc)));
@@ -366,7 +375,8 @@ ArmV8KvmCPU::getSysRegMap() const
         // Only add implemented registers that we are going to be able
         // to write.
         if (implemented && writeable)
-            sysRegMap.emplace_back(reg, idx, miscRegName[idx]);
+            sysRegMap.emplace_back(reg, idx, miscRegName[idx],
+                deviceRegSet.find(idx) != deviceRegSet.end());
     }
 
     return sysRegMap;
diff --git a/src/arch/arm/kvm/armv8_cpu.hh b/src/arch/arm/kvm/armv8_cpu.hh
index 63e03908f..101ccc211 100644
--- a/src/arch/arm/kvm/armv8_cpu.hh
+++ b/src/arch/arm/kvm/armv8_cpu.hh
@@ -40,6 +40,7 @@
 #ifndef __ARCH_ARM_KVM_ARMV8_CPU_HH__
 #define __ARCH_ARM_KVM_ARMV8_CPU_HH__
 
+#include <set>
 #include <vector>
 
 #include "arch/arm/intregs.hh"
@@ -107,8 +108,9 @@ class ArmV8KvmCPU : public BaseArmKvmCPU
 
     /** Mapping between misc registers in gem5 and registers in KVM */
     struct MiscRegInfo {
-        MiscRegInfo(uint64_t _kvm, MiscRegIndex _idx, const char *_name)
-            : kvm(_kvm), idx(_idx), name(_name) {}
+        MiscRegInfo(uint64_t _kvm, MiscRegIndex _idx, const char *_name,
+                    bool _is_device = false)
+            : kvm(_kvm), idx(_idx), name(_name), is_device(_is_device) {}
 
         /** Register index in KVM */
         uint64_t kvm;
@@ -116,6 +118,8 @@ class ArmV8KvmCPU : public BaseArmKvmCPU
         MiscRegIndex idx;
         /** Name to use in debug dumps */
         const char *name;
+        /** is device register? (needs 'effectful' state update) */
+        bool is_device;
     };
 
     /**
@@ -132,9 +136,11 @@ class ArmV8KvmCPU : public BaseArmKvmCPU
 
     /** Mapping between gem5 integer registers and integer registers in kvm */
     static const std::vector<ArmV8KvmCPU::IntRegInfo> intRegMap;
-    /** Mapping between gem5 misc registers registers and registers in kvm */
+    /** Mapping between gem5 misc registers and registers in kvm */
     static const std::vector<ArmV8KvmCPU::MiscRegInfo> miscRegMap;
-    /** Mapping between gem5 ID misc registers registers and registers in kvm */
+    /** Device registers (needing "effectful" MiscReg writes) */
+    static const std::set<MiscRegIndex> deviceRegSet;
+    /** Mapping between gem5 ID misc registers and registers in kvm */
     static const std::vector<ArmV8KvmCPU::MiscRegInfo> miscRegIdMap;
 
     /** Cached mapping between system registers in kvm and misc regs in gem5 */