arch, arm: Preserve TLB bootUncacheability when switching CPUs

The ARM TLBs have a bootUncacheability flag used to make some loads
and stores become uncacheable when booting in FS mode. Later the
flag is cleared to let those loads and stores operate as normal.  When
doing a takeOverFrom(), this flag's state is not preserved and is
momentarily reset until the CPSR is touched. On single core runs this
is a non-issue. On multi-core runs this can lead to crashes on the O3
CPU model from the following series of events:
 1) takeOverFrom executed to switch from Atomic -> O3
 2) All bootUncacheability flags are reset to true
 3) Core2 tries to execute a load covered by bootUncacheability, it
    is flagged as uncacheable
 4) Core2's load needs to replay due to a pipeline flush
 3) Core1 core does an action on CPSR
 4) The handling code for CPSR then checks all other cores
    to determine if bootUncacheability can be set to false
 5) Asynchronously set bootUncacheability on all cores to false
 6) Core2 replays load previously set as uncacheable and notices
    it is now flagged as cacheable, leads to a panic.
This patch implements takeOverFrom() functionality for the ARM TLBs
to preserve flag values when switching from atomic -> detailed.

src/arch/alpha/tlb.hh

@@ -87,6 +87,8 @@ class TLB : public BaseTLB
     TLB(const Params *p);
     virtual ~TLB();
 
+    void takeOverFrom(BaseTLB *otlb) {}
+
     virtual void regStats();
 
     int getsize() const { return size; }

src/arch/arm/tlb.cc

@@ -353,6 +353,30 @@ TLB::drainResume()
     miscRegValid = false;
 }
 
+void
+TLB::takeOverFrom(BaseTLB *_otlb)
+{
+    TLB *otlb = dynamic_cast<TLB*>(_otlb);
+    /* Make sure we actually have a valid type */
+    if (otlb) {
+        _attr = otlb->_attr;
+        haveLPAE = otlb->haveLPAE;
+        directToStage2 = otlb->directToStage2;
+        stage2Req = otlb->stage2Req;
+        bootUncacheability = otlb->bootUncacheability;
+
+        /* Sync the stage2 MMU if they exist in both
+         * the old CPU and the new
+         */
+        if (!isStage2 &&
+            stage2Tlb && otlb->stage2Tlb) {
+            stage2Tlb->takeOverFrom(otlb->stage2Tlb);
+        }
+    } else {
+        panic("Incompatible TLB type!");
+    }
+}
+
 void
 TLB::serialize(ostream &os)
 {

src/arch/arm/tlb.hh

@@ -155,6 +155,8 @@ class TLB : public BaseTLB
 
     virtual ~TLB();
 
+    void takeOverFrom(BaseTLB *otlb);
+
     /// setup all the back pointers
     virtual void init();
 

src/arch/mips/tlb.hh

@@ -87,6 +87,9 @@ class TLB : public BaseTLB
     int probeEntry(Addr vpn,uint8_t) const;
     MipsISA::PTE *getEntry(unsigned) const;
     virtual ~TLB();
+
+    void takeOverFrom(BaseTLB *otlb) {}
+
     int smallPages;
     int getsize() const { return size; }
 

src/arch/power/tlb.hh

@@ -130,6 +130,8 @@ class TLB : public BaseTLB
     TLB(const Params *p);
     virtual ~TLB();
 
+    void takeOverFrom(BaseTLB *otlb) {}
+
     int probeEntry(Addr vpn,uint8_t) const;
     PowerISA::PTE *getEntry(unsigned) const;
 

src/arch/sparc/tlb.hh

@@ -154,6 +154,8 @@ class TLB : public BaseTLB
     typedef SparcTLBParams Params;
     TLB(const Params *p);
 
+    void takeOverFrom(BaseTLB *otlb) {}
+
     void
     demapPage(Addr vaddr, uint64_t asn)
     {

src/arch/x86/tlb.hh

@@ -75,6 +75,8 @@ namespace X86ISA
         typedef X86TLBParams Params;
         TLB(const Params *p);
 
+        void takeOverFrom(BaseTLB *otlb) {}
+
         TlbEntry *lookup(Addr va, bool update_lru = true);
 
         void setConfigAddress(uint32_t addr);

src/cpu/base.cc

@@ -432,6 +432,8 @@ BaseCPU::takeOverFrom(BaseCPU *oldCPU)
             old_dtb_port->unbind();
             new_dtb_port->bind(slavePort);
         }
+        newTC->getITBPtr()->takeOverFrom(oldTC->getITBPtr());
+        newTC->getDTBPtr()->takeOverFrom(oldTC->getDTBPtr());
 
         // Checker whether or not we have to transfer CheckerCPU
         // objects over in the switch
@@ -447,6 +449,9 @@ BaseCPU::takeOverFrom(BaseCPU *oldCPU)
             BaseMasterPort *new_checker_dtb_port =
                 newChecker->getDTBPtr()->getMasterPort();
 
+            newChecker->getITBPtr()->takeOverFrom(oldChecker->getITBPtr());
+            newChecker->getDTBPtr()->takeOverFrom(oldChecker->getDTBPtr());
+
             // Move over any table walker ports if they exist for checker
             if (new_checker_itb_port) {
                 assert(!new_checker_itb_port->isConnected());

src/sim/tlb.hh

@@ -69,6 +69,11 @@ class BaseTLB : public SimObject
      */
     virtual void flushAll() = 0;
 
+    /**
+     * Take over from an old tlb context
+     */
+    virtual void takeOverFrom(BaseTLB *otlb) = 0;
+
     /**
      * Get the table walker master port if present. This is used for
      * migrating port connections during a CPU takeOverFrom()