changeset 22f08c96bf7f in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=22f08c96bf7f
description:
kvm: Support timing accesses for KVM cpu
This patch enables timing accesses for KVM cpu. A new state,
RunningMMIOPending, is added to indicate that there are outstanding
timing
requests generated by KVM in the system. KVM's tick() is disabled and
the
simulation does not enter into KVM until all outstanding timing
requests have
completed. The main motivation for this is to allow KVM CPU to perform
MMIO
in Ruby, since Ruby does not support atomic accesses.
diffstat:
src/cpu/kvm/base.cc | 129 +++++++++++++++++++++++++++++++++++++++++-------
src/cpu/kvm/base.hh | 56 ++++++++++++++++----
src/cpu/kvm/x86_cpu.cc | 14 ++--
3 files changed, 159 insertions(+), 40 deletions(-)
diffs (truncated from 373 to 300 lines):
diff -r 85011e8eaad9 -r 22f08c96bf7f src/cpu/kvm/base.cc
--- a/src/cpu/kvm/base.cc Tue Sep 13 23:18:34 2016 -0400
+++ b/src/cpu/kvm/base.cc Tue Sep 13 23:20:03 2016 -0400
@@ -170,6 +170,76 @@
schedule(startupEvent, curTick());
}
+BaseKvmCPU::Status
+BaseKvmCPU::KVMCpuPort::nextIOState() const
+{
+ return (activeMMIOReqs || pendingMMIOPkts.size())
+ ? RunningMMIOPending : RunningServiceCompletion;
+}
+
+Tick
+BaseKvmCPU::KVMCpuPort::submitIO(PacketPtr pkt)
+{
+ if (cpu->system->isAtomicMode()) {
+ Tick delay = sendAtomic(pkt);
+ delete pkt->req;
+ delete pkt;
+ return delay;
+ } else {
+ if (pendingMMIOPkts.empty() && sendTimingReq(pkt)) {
+ activeMMIOReqs++;
+ } else {
+ pendingMMIOPkts.push(pkt);
+ }
+ // Return value is irrelevant for timing-mode accesses.
+ return 0;
+ }
+}
+
+bool
+BaseKvmCPU::KVMCpuPort::recvTimingResp(PacketPtr pkt)
+{
+ DPRINTF(KvmIO, "KVM: Finished timing request\n");
+
+ delete pkt->req;
+ delete pkt;
+ activeMMIOReqs--;
+
+ // We can switch back into KVM when all pending and in-flight MMIO
+ // operations have completed.
+ if (!(activeMMIOReqs || pendingMMIOPkts.size())) {
+ DPRINTF(KvmIO, "KVM: Finished all outstanding timing requests\n");
+ cpu->finishMMIOPending();
+ }
+ return true;
+}
+
+void
+BaseKvmCPU::KVMCpuPort::recvReqRetry()
+{
+ DPRINTF(KvmIO, "KVM: Retry for timing request\n");
+
+ assert(pendingMMIOPkts.size());
+
+ // Assuming that we can issue infinite requests this cycle is a bit
+ // unrealistic, but it's not worth modeling something more complex in
+ // KVM.
+ while (pendingMMIOPkts.size() && sendTimingReq(pendingMMIOPkts.front())) {
+ pendingMMIOPkts.pop();
+ activeMMIOReqs++;
+ }
+}
+
+void
+BaseKvmCPU::finishMMIOPending()
+{
+ assert(_status = RunningMMIOPending);
+ assert(!tickEvent.scheduled());
+
+ _status = RunningServiceCompletion;
+ schedule(tickEvent, nextCycle());
+}
+
void
BaseKvmCPU::startupThread()
{
@@ -329,6 +399,12 @@
"requesting drain.\n");
return DrainState::Draining;
+ case RunningMMIOPending:
+ // We need to drain since there are in-flight timing accesses
+ DPRINTF(Drain, "KVM CPU is waiting for timing accesses to complete, "
+ "requesting drain.\n");
+ return DrainState::Draining;
+
case RunningService:
// We need to drain since the CPU is waiting for service (e.g., MMIOs)
DPRINTF(Drain, "KVM CPU is waiting for service, requesting drain.\n");
@@ -425,9 +501,9 @@
void
BaseKvmCPU::verifyMemoryMode() const
{
- if (!(system->isAtomicMode() && system->bypassCaches())) {
+ if (!(system->bypassCaches())) {
fatal("The KVM-based CPUs requires the memory system to be in the "
- "'atomic_noncaching' mode.\n");
+ "'noncaching' mode.\n");
}
}
@@ -536,7 +612,7 @@
BaseKvmCPU::tick()
{
Tick delay(0);
- assert(_status != Idle);
+ assert(_status != Idle && _status != RunningMMIOPending);
switch (_status) {
case RunningService:
@@ -620,7 +696,7 @@
}
// Schedule a new tick if we are still running
- if (_status != Idle)
+ if (_status != Idle && _status != RunningMMIOPending)
schedule(tickEvent, clockEdge(ticksToCycles(delay)));
}
@@ -629,8 +705,9 @@
{
// By default, the only thing we need to drain is a pending IO
// operation which assumes that we are in the
- // RunningServiceCompletion state.
- assert(_status == RunningServiceCompletion);
+ // RunningServiceCompletion or RunningMMIOPending state.
+ assert(_status == RunningServiceCompletion ||
+ _status == RunningMMIOPending);
// Deliver the data from the pending IO operation and immediately
// exit.
@@ -922,9 +999,12 @@
return handleKvmExitException();
case KVM_EXIT_IO:
- _status = RunningServiceCompletion;
+ {
++numIO;
- return handleKvmExitIO();
+ Tick ticks = handleKvmExitIO();
+ _status = dataPort.nextIOState();
+ return ticks;
+ }
case KVM_EXIT_HYPERCALL:
++numHypercalls;
@@ -942,15 +1022,21 @@
return 0;
case KVM_EXIT_MMIO:
- _status = RunningServiceCompletion;
+ {
/* Service memory mapped IO requests */
DPRINTF(KvmIO, "KVM: Handling MMIO (w: %u, addr: 0x%x, len: %u)\n",
_kvmRun->mmio.is_write,
_kvmRun->mmio.phys_addr, _kvmRun->mmio.len);
++numMMIO;
- return doMMIOAccess(_kvmRun->mmio.phys_addr, _kvmRun->mmio.data,
- _kvmRun->mmio.len, _kvmRun->mmio.is_write);
+ Tick ticks = doMMIOAccess(_kvmRun->mmio.phys_addr, _kvmRun->mmio.data,
+ _kvmRun->mmio.len, _kvmRun->mmio.is_write);
+ // doMMIOAccess could have triggered a suspend, in which case we don't
+ // want to overwrite the _status.
+ if (_status != Idle)
+ _status = dataPort.nextIOState();
+ return ticks;
+ }
case KVM_EXIT_IRQ_WINDOW_OPEN:
return handleKvmExitIRQWindowOpen();
@@ -1026,30 +1112,33 @@
ThreadContext *tc(thread->getTC());
syncThreadContext();
- Request mmio_req(paddr, size, Request::UNCACHEABLE, dataMasterId());
- mmio_req.setContext(tc->contextId());
+ RequestPtr mmio_req = new Request(paddr, size, Request::UNCACHEABLE,
+ dataMasterId());
+ mmio_req->setContext(tc->contextId());
// Some architectures do need to massage physical addresses a bit
// before they are inserted into the memory system. This enables
// APIC accesses on x86 and m5ops where supported through a MMIO
// interface.
BaseTLB::Mode tlb_mode(write ? BaseTLB::Write : BaseTLB::Read);
- Fault fault(tc->getDTBPtr()->finalizePhysical(&mmio_req, tc, tlb_mode));
+ Fault fault(tc->getDTBPtr()->finalizePhysical(mmio_req, tc, tlb_mode));
if (fault != NoFault)
warn("Finalization of MMIO address failed: %s\n", fault->name());
const MemCmd cmd(write ? MemCmd::WriteReq : MemCmd::ReadReq);
- Packet pkt(&mmio_req, cmd);
- pkt.dataStatic(data);
+ PacketPtr pkt = new Packet(mmio_req, cmd);
+ pkt->dataStatic(data);
- if (mmio_req.isMmappedIpr()) {
+ if (mmio_req->isMmappedIpr()) {
// We currently assume that there is no need to migrate to a
// different event queue when doing IPRs. Currently, IPRs are
// only used for m5ops, so it should be a valid assumption.
const Cycles ipr_delay(write ?
- TheISA::handleIprWrite(tc, &pkt) :
- TheISA::handleIprRead(tc, &pkt));
+ TheISA::handleIprWrite(tc, pkt) :
+ TheISA::handleIprRead(tc, pkt));
threadContextDirty = true;
+ delete pkt->req;
+ delete pkt;
return clockPeriod() * ipr_delay;
} else {
// Temporarily lock and migrate to the event queue of the
@@ -1057,7 +1146,7 @@
// access if running in multi-core mode.
EventQueue::ScopedMigration migrate(vm.eventQueue());
- return dataPort.sendAtomic(&pkt);
+ return dataPort.submitIO(pkt);
}
}
diff -r 85011e8eaad9 -r 22f08c96bf7f src/cpu/kvm/base.hh
--- a/src/cpu/kvm/base.hh Tue Sep 13 23:18:34 2016 -0400
+++ b/src/cpu/kvm/base.hh Tue Sep 13 23:20:03 2016 -0400
@@ -44,6 +44,7 @@
#include <csignal>
#include <memory>
+#include <queue>
#include "base/statistics.hh"
#include "cpu/kvm/perfevent.hh"
@@ -110,6 +111,12 @@
Counter totalInsts() const override;
Counter totalOps() const override;
+ /**
+ * Callback from KvmCPUPort to transition the CPU out of RunningMMIOPending
+ * when all timing requests have completed.
+ */
+ void finishMMIOPending();
+
/** Dump the internal state to the terminal. */
virtual void dump() const;
@@ -152,6 +159,7 @@
* Running;
* RunningService;
* RunningServiceCompletion;
+ * RunningMMIOPending;
*
* Idle -> Idle;
* Idle -> Running [label="activateContext()", URL="\ref
activateContext"];
@@ -161,6 +169,8 @@
* Running -> Idle [label="drain()", URL="\ref drain"];
* Idle -> Running [label="drainResume()", URL="\ref drainResume"];
* RunningService -> RunningServiceCompletion
[label="handleKvmExit()", URL="\ref handleKvmExit"];
+ * RunningService -> RunningMMIOPending [label="handleKvmExit()",
URL="\ref handleKvmExit"];
+ * RunningMMIOPending -> RunningServiceCompletion
[label="finishMMIOPending()", URL="\ref finishMMIOPending"];
* RunningServiceCompletion -> Running [label="tick()", URL="\ref
tick"];
* RunningServiceCompletion -> RunningService [label="tick()",
URL="\ref tick"];
* }
@@ -190,12 +200,21 @@
* after running service is determined in handleKvmExit() and
* depends on what kind of service the guest requested:
* <ul>
- * <li>IO/MMIO: RunningServiceCompletion
+ * <li>IO/MMIO (Atomic): RunningServiceCompletion
+ * <li>IO/MMIO (Timing): RunningMMIOPending
* <li>Halt: Idle
* <li>Others: Running
* </ul>
*/
RunningService,
+ /** Timing MMIO request in flight or stalled.
+ *
+ * The VM has requested IO/MMIO and we are in timing mode. A timing
+ * request is either stalled (and will be retried with recvReqRetry())
+ * or it is in flight. After the timing request is complete, the CPU
+ * will transition to the RunningServiceCompletion state.
+ */
+ RunningMMIOPending,
/** Service completion in progress.
*
* The VM has requested service that requires KVM to be
@@ -543,28 +562,39 @@
/**
- * KVM memory port. Uses the default MasterPort behavior, but
- * panics on timing accesses.
+ * KVM memory port. Uses default MasterPort behavior and provides an
+ * interface for KVM to transparently submit atomic or timing requests.
*/
class KVMCpuPort : public MasterPort
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