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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.
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Only map memories into the KVM guest address space that are
marked as usable by KVM. Create BackingStoreEntry class
containing flags for is_conf_reported, in_addr_map, and
kvm_map.
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In general, the ThreadID parameter is unnecessary in the memory system
as the ContextID is what is used for the purposes of locks/wakeups.
Since we allocate sequential ContextIDs for each thread on MT-enabled
CPUs, ThreadID is unnecessary as the CPUs can identify the requesting
thread through sideband info (SenderState / LSQ entries) or ContextID
offset from the base ContextID for a cpu.
This is a re-spin of 20264eb after the revert (bd1c6789) and includes
some fixes of that commit.
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The following patches had unexpected interactions with the current
upstream code and have been reverted for now:
e07fd01651f3: power: Add support for power models
831c7f2f9e39: power: Low-power idle power state for idle CPUs
4f749e00b667: power: Add power states to ClockedObject
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
--HG--
extra : amend_source : 0b6fb073c6bbc24be533ec431eb51fbf1b269508
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In general, the ThreadID parameter is unnecessary in the memory system
as the ContextID is what is used for the purposes of locks/wakeups.
Since we allocate sequential ContextIDs for each thread on MT-enabled
CPUs, ThreadID is unnecessary as the CPUs can identify the requesting
thread through sideband info (SenderState / LSQ entries) or ContextID
offset from the base ContextID for a cpu.
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This changeset adds an option to force the kvm-based CPUs to always
synchronize the gem5 thread context representation on entry/exit into
the kernel. This is very useful for debugging. Unfortunately, it is
also the only way to get reliable register contents when using remote
gdb functionality. The long-term solution for the latter would be to
implement a kvm-specific thread context.
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Alexandru Dutu <alexandru.dutu@amd.com>
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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>
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Since the last round of fixes a few new issues have snuck in. We
should consider switching the regression runs to clang.
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Result of running 'hg m5style --skip-all --fix-control -a'.
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This patch moves away from using M5_ATTR_OVERRIDE and the m5::hashmap
(and similar) abstractions, as these are no longer needed with gcc 4.7
and clang 3.1 as minimum compiler versions.
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Changes wakeup functionality so that only specific threads on SMT
capable cpus are woken.
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Adds per-thread interrupt controllers and thread/context logic
so that interrupts properly get routed in SMT systems.
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The drain() call currently passes around a DrainManager pointer, which
is now completely pointless since there is only ever one global
DrainManager in the system. It also contains vestiges from the time
when SimObjects had to keep track of their child objects that needed
draining.
This changeset moves all of the DrainState handling to the Drainable
base class and changes the drain() and drainResume() calls to reflect
this. Particularly, the drain() call has been updated to take no
parameters (the DrainManager argument isn't needed) and return a
DrainState instead of an unsigned integer (there is no point returning
anything other than 0 or 1 any more). Drainable objects should return
either DrainState::Draining (equivalent to returning 1 in the old
system) if they need more time to drain or DrainState::Drained
(equivalent to returning 0 in the old system) if they are already in a
consistent state. Returning DrainState::Running is considered an
error.
Drain done signalling is now done through the signalDrainDone() method
in the Drainable class instead of using the DrainManager directly. The
new call checks if the state of the object is DrainState::Draining
before notifying the drain manager. This means that it is safe to call
signalDrainDone() without first checking if the simulator has
requested draining. The intention here is to reduce the code needed to
implement draining in simple objects.
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Objects that are can be serialized are supposed to inherit from the
Serializable class. This class is meant to provide a unified API for
such objects. However, so far it has mainly been used by SimObjects
due to some fundamental design limitations. This changeset redesigns
to the serialization interface to make it more generic and hide the
underlying checkpoint storage. Specifically:
* Add a set of APIs to serialize into a subsection of the current
object. Previously, objects that needed this functionality would
use ad-hoc solutions using nameOut() and section name
generation. In the new world, an object that implements the
interface has the methods serializeSection() and
unserializeSection() that serialize into a named /subsection/ of
the current object. Calling serialize() serializes an object into
the current section.
* Move the name() method from Serializable to SimObject as it is no
longer needed for serialization. The fully qualified section name
is generated by the main serialization code on the fly as objects
serialize sub-objects.
* Add a scoped ScopedCheckpointSection helper class. Some objects
need to serialize data structures, that are not deriving from
Serializable, into subsections. Previously, this was done using
nameOut() and manual section name generation. To simplify this,
this changeset introduces a ScopedCheckpointSection() helper
class. When this class is instantiated, it adds a new /subsection/
and subsequent serialization calls during the lifetime of this
helper class happen inside this section (or a subsection in case
of nested sections).
* The serialize() call is now const which prevents accidental state
manipulation during serialization. Objects that rely on modifying
state can use the serializeOld() call instead. The default
implementation simply calls serialize(). Note: The old-style calls
need to be explicitly called using the
serializeOld()/serializeSectionOld() style APIs. These are used by
default when serializing SimObjects.
* Both the input and output checkpoints now use their own named
types. This hides underlying checkpoint implementation from
objects that need checkpointing and makes it easier to change the
underlying checkpoint storage code.
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This changeset adds support for aarch64 in kvm. The CPU module
supports both checkpointing and online CPU model switching as long as
no devices are simulated by the host kernel. It currently has the
following limitations:
* The system register based generic timer can only be simulated by
the host kernel. Workaround: Use a memory mapped timer instead to
simulate the timer in gem5.
* Simulating devices (e.g., the generic timer) in the host kernel
requires that the host kernel also simulates the GIC.
* ID registers in the host and in gem5 must match for switching
between simulated CPUs and KVM. This is particularly important
for ID registers describing memory system capabilities (e.g.,
ASID size, physical address size).
* Switching between a virtualized CPU and a simulated CPU is
currently not supported if in-kernel device emulation is
used. This could be worked around by adding support for switching
to the gem5 (e.g., the KvmGic) side of the device models. A
simpler workaround is to avoid in-kernel device models
altogether.
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This changeset adds a GIC implementation that uses the kernel's
built-in support for simulating the interrupt controller. Since there
is currently no support for state transfer between gem5 and the
kernel, the device model does not support serialization and CPU
switching (which would require switching to a gem5-simulated GIC).
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There are cases (particularly when attaching GDB) when instruction
events are scheduled at the current instruction tick. This used to
trigger an assertion error in kvm. This changeset adds a check for
this condition and forces KVM to do a quick entry that completes any
pending IO operations, but does not execute any new instructions,
before servicing the event. We could check if we need to enter KVM at
all, but forcing a quick entry is makes the code slightly cleaner and
does not hurt correctness (performance is hardly an issue in these
cases).
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This changeset moves the ARM-specific KVM CPU implementation to
arch/arm/kvm/. This change is expected to keep the source tree
somewhat cleaner as we start adding support for ARMv8 and KVM
in-kernel interrupt controller simulation.
--HG--
rename : src/cpu/kvm/ArmKvmCPU.py => src/arch/arm/kvm/ArmKvmCPU.py
rename : src/cpu/kvm/arm_cpu.cc => src/arch/arm/kvm/arm_cpu.cc
rename : src/cpu/kvm/arm_cpu.hh => src/arch/arm/kvm/arm_cpu.hh
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The register dumping code in kvm tries to print the bytes in large
registers (128 bits and larger) instead of printing them as hex. This
changeset fixes that.
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Protect x86-specific APIs in KvmVM with compile-time guards to avoid
breaking ARM builds.
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This patch fixes a long-standing isue with the port flow
control. Before this patch the retry mechanism was shared between all
different packet classes. As a result, a snoop response could get
stuck behind a request waiting for a retry, even if the send/recv
functions were split. This caused message-dependent deadlocks in
stress-test scenarios.
The patch splits the retry into one per packet (message) class. Thus,
sendTimingReq has a corresponding recvReqRetry, sendTimingResp has
recvRespRetry etc. Most of the changes to the code involve simply
clarifying what type of request a specific object was accepting.
The biggest change in functionality is in the cache downstream packet
queue, facing the memory. This queue was shared by requests and snoop
responses, and it is now split into two queues, each with their own
flow control, but the same physical MasterPort. These changes fixes
the previously seen deadlocks.
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This patch tidies up how we create and set the fields of a Request. In
essence it tries to use the constructor where possible (as opposed to
setPhys and setVirt), thus avoiding spreading the information across a
number of locations. In fact, setPhys is made private as part of this
patch, and a number of places where we callede setVirt instead uses
the appropriate constructor.
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This patch adds methods in KvmCPU model to handle KVM exits caused by syscall
instructions and page faults. These types of exits will be encountered if
KvmCPU is run in SE mode.
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activate(), suspend(), and halt() used on thread contexts had an optional
delay parameter. However this parameter was often ignored. Also, when used,
the delay was seemily arbitrarily set to 0 or 1 cycle (no other delays were
ever specified). This patch removes the delay parameter and 'Events'
associated with them across all ISAs and cores. Unused activate logic
is also removed.
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Simulating a SMP or multicore requires devices to be shared between
multiple KVM vCPUs. This means that locking is required when accessing
devices. This changeset adds the necessary locking to allow devices to
execute correctly. It is implemented by temporarily migrating the KVM
CPU to the VM's (and devices) event queue when handling
MMIO. Similarly, the VM migrates to the interrupt controller's event
queue when delivering an interrupt.
The support for fast-forwarding of multicore simulations added by this
changeset assumes that all devices in a system are simulated in the
same thread and each vCPU has its own thread. Special care must be
taken to ensure that devices living under the CPU in the object
hierarchy (e.g., the interrupt controller) do not inherit the parent
CPUs thread and are assigned to device thread. The KvmVM object is
assumed to live in the same thread as the other devices in the system.
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KVM used to use two signals, one for instruction count exits and one
for timer exits. There is really no need to distinguish between the
two since they only trigger exits from KVM. This changeset unifies and
renames the signals and adds a method, kick(), that can be used to
raise the control signal in the vCPU thread. It also removes the early
timer warning since we do not normally see if the signal was
delivered.
--HG--
extra : rebase_source : cd0e45ca90894c3d6f6aa115b9b06a1d8f0fda4d
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gem5 seems to store the PC as RIP+CS_BASE. This is not what KVM
expects, so we need to subtract CS_BASE prior to transferring the PC
into KVM. This changeset adds the necessary PC manipulation and
refactors thread context updates slightly to avoid reading registers
multiple times from KVM.
--HG--
extra : rebase_source : 3f0569dca06a1fcd8694925f75c8918d954ada44
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This changeset adds support for INIT and STARTUP IPI handling. We
currently handle both of these interrupts in gem5 and transfer the
state to KVM. Since we do not have a BIOS loaded, we pretend that the
INIT interrupt suspends the CPU after reset.
--HG--
extra : rebase_source : 7f3b25f3801d68f668b6cd91eaf50d6f48ee2a6a
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When transferring segment registers into kvm, we need to find the
value of the unusable bit. We used to assume that this could be
inferred from the selector since segments are generally unusable if
their selector is 0. This assumption breaks in some weird corner
cases. Instead, we just assume that segments are always usable. This
is what qemu does so it should work.
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Signal handlers in KVM are controlled per thread and should be
initialized from the thread that is going to execute the CPU. This
changeset moves the initialization call from startup() to
startupThread().
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The introduction of parallel event queues added most of the support
needed to run multiple VMs (systems) within the same gem5
instance. This changeset fixes up signal delivery so that KVM's
control signals are delivered to the thread that executes the CPU's
event queue. Specifically:
* Timers and counters are now initialized from a separate method
(startupThread) that is scheduled as the first event in the
thread-specific event queue. This ensures that they are
initialized from the thread that is going to execute the CPUs
event queue and enables signal delivery to the right thread when
exiting from KVM.
* The POSIX-timer-based KVM timer (used to force exits from KVM) has
been updated to deliver signals to the thread that's executing KVM
instead of the process (thread is undefined in that case). This
assumes that the timer is instantiated from the thread that is
going to execute the KVM vCPU.
* Signal masking is now done using pthread_sigmask instead of
sigprocmask. The behavior of the latter is undefined in threaded
applications.
* Since signal masks can be inherited, make sure to actively unmask
the control signals when setting up the KVM signal mask.
There are currently no facilities to multiplex between multiple KVM
CPUs in the same event queue, we are therefore limited to
configurations where there is only one KVM CPU per event queue. In
practice, this means that multi-system configurations can be
simulated, but not multiple CPUs in a shared-memory configuration.
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The performance counting framework in Linux 3.2 and onwards supports
an attribute to exclude events generated by the host when running
KVM. Setting this attribute allows us to get more reliable
measurements of the guest machine. For example, on a highly loaded
system, the instruction counts from the guest can be severely
distorted by the host kernel (e.g., by page fault handlers).
This changeset introduces a check for the attribute and enables it in
the KVM CPU if present.
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This patch adds support for simulating with multiple threads, each of
which operates on an event queue. Each sim object specifies which eventq
is would like to be on. A custom barrier implementation is being added
using which eventqs synchronize.
The patch was tested in two different configurations:
1. ruby_network_test.py: in this simulation L1 cache controllers receive
requests from the cpu. The requests are replied to immediately without
any communication taking place with any other level.
2. twosys-tsunami-simple-atomic: this configuration simulates a client-server
system which are connected by an ethernet link.
We still lack the ability to communicate using message buffers or ports. But
other things like simulation start and end, synchronizing after every quantum
are working.
Committed by: Nilay Vaish
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When handling IPR accesses in doMMIOAccess, the KVM CPU used
clockEdge() to convert between cycles and ticks. This is incorrect
since doMMIOAccess is supposed to return a latency in ticks rather
than when the access is done. This changeset fixes this issue by
returning clockPeriod() * ipr_delay instead.
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This changset adds calls to the service the instruction event queues
that accidentally went missing from commit [0063c7dd18ec]. The
original commit only included the code needed to schedule instruction
stops from KVM and missed the functionality to actually service the
events.
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Instruction events are currently ignored when executing in KVM. This
changeset adds support for triggering KVM exits based on instruction
counts using hardware performance counters. Depending on the
underlying performance counter implementation, there might be some
inaccuracies due to instructions being counted in the host kernel when
entering/exiting KVM.
Due to limitations/bugs in Linux's performance counter interface, we
can't reliably change the period of an overflow counter. We work
around this issue by detaching and reattaching the counter if we need
to reconfigure it.
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This changeset adds support for synchronizing the FPU and SIMD state
of a virtual x86 CPU with gem5. It supports both the XSave API and the
KVM_(GET|SET)_FPU kernel API. The XSave interface can be disabled
using the useXSave parameter (in case of kernel
issues). Unfortunately, KVM_(GET|SET)_FPU interface seems to be buggy
in some kernels (specifically, the MXCSR register isn't always
synchronized), which means that it might not be possible to
synchronize MXCSR on old kernels without the XSave interface.
This changeset depends on the __float80 type in gcc and might not
build using llvm.
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There are cases when the segment registers in gem5 are not compatible
with VMX. This changeset works around all known such issues. Specifically:
* The accessed bits in CS, SS, DD, ES, FS, GS are forced to 1.
* The busy bit in TR is forced to 1.
* The protection level of SS is forced to the same protection level as
CS. The difference /seems/ to be caused by a bug in gem5's x86
implementation.
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This changeset adds support for KVM on x86. Full support is split
across a number of commits since some features are relatively
complex. This changeset includes support for:
* Integer state synchronization (including segment regs)
* CPUID (gem5's CPUID values are inserted into KVM)
* x86 legacy IO (remapped and handled by gem5's memory system)
* Memory mapped IO
* PCI
* MSRs
* State dumping
Most of the functionality is fairly straight forward. There are some
quirks to support PCI enumerations since this is done in the TLB(!) in
the simulated CPUs. We currently replicate some of that code.
Unlike the ARM implementation, the x86 implementation of the virtual
CPU does not use the cycles hardware counter. KVM on x86 simulates the
time stamp counter (TSC) in the kernel. If we just measure host cycles
using perfevent, we might end up measuring a slightly different number
of cycles. If we don't get the cycle accounting right, we might end up
rewinding the TSC, with all kinds of chaos as a result.
An additional feature of the KVM CPU on x86 is extended state
dumping. This enables Python scripts controlling the simulator to
request dumping of a subset of the processor state. The following
methods are currenlty supported:
* dumpFpuRegs
* dumpIntRegs
* dumpSpecRegs
* dumpDebugRegs
* dumpXCRs
* dumpXSave
* dumpVCpuEvents
* dumpMSRs
Known limitations:
* M5 ops are currently not supported.
* FPU synchronization is not supported (only affects CPU switching).
Both of the limitations will be addressed in separate commits.
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The KVM base class incorrectly assumed that handleIprRead and
handleIprWrite both return ticks. This is not the case, instead they
return cycles. This changeset converts the returned cycles to ticks
when handling IPR accesses.
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There is a possibility that the timespec used to arm a timer becomes
zero if the number of ticks used when arming a timer is close to the
resolution of the timer. Due to the semantics of POSIX timers, this
actually disarms the timer. This changeset fixes this issue by
eliminating the rounding error (we always round away from zero
now). It also reuses the minimum number of cycles, which were
previously only used for cycle-based timers, to calculate a more
useful resolution.
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Reuse the address finalization code in the TLB instead of replicating
it when handling MMIO. This patch also adds support for injecting
memory mapped IPR requests into the memory system.
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This changeset adds the following stats to KVM:
* numVMHalfEntries: Number of entries into KVM to finalize pending
IO operations without executing guest instructions. These typically
happen as a result of a drain where the guest must finalize some
operations before the guest state is consistent.
* numExitSignal: Number of VM exits that have been triggered by a
signal. These usually happen as a result of the timer that limits
the time spent in KVM.
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We used to use the KVM CPU's clock to specify the host frequency. This
was not ideal for several reasons. One of them being that the clock
parameter of a CPU determines the frequency of some of the components
connected to the CPU. This changeset adds a separate hostFreq
parameter that should be used to specify the host frequency until we
add code to autodetect it. The hostFactor should still be used to
specify the conversion factor between the host performance and that of
the simulated system.
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We currently execute instructions in the guest and then handle any IO
request right after we break out of the virtualized environment. This
has the effect of executing IO requests in the exact same tick as the
first instruction in the sequence that was just run. There seem to be
cases where this simplification upsets some timing-sensitive devices.
This changeset splits execute and IO (and other services) across
multiple ticks. This is implemented by adding a separate
RunningService state to the CPU state machine. When a VM requires
service, it enters into this state and pending IO is then serviced in
the future instead of immediately. The delay between getting the
request and servicing it depends on the number of cycles executed in
the guest, which allows other components to catch up with the CPU.
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Update the system's totalNumInst counter when exiting from KVM and
maintain an internal absolute instruction count instead of relying on
the one from perf.
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Some architectures have special registers in the guest that can be
used to do cycle accounting. This is generally preferrable since the
prevents the guest from seeing a non-monotonic clock. This changeset
adds a virtual method, getHostCycles(), that the architecture-specific
code can override to implement this functionallity. The default
implementation uses the hwCycles counter.
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