gem5/src/cpu/minor/exec_context.hh
Brandon Potter a5802c823f syscall_emul: [patch 13/22] add system call retry capability
This changeset adds functionality that allows system calls to retry without
affecting thread context state such as the program counter or register values
for the associated thread context (when system calls return with a retry
fault).

This functionality is needed to solve problems with blocking system calls
in multi-process or multi-threaded simulations where information is passed
between processes/threads. Blocking system calls can cause deadlock because
the simulator itself is single threaded. There is only a single thread
servicing the event queue which can cause deadlock if the thread hits a
blocking system call instruction.

To illustrate the problem, consider two processes using the producer/consumer
sharing model. The processes can use file descriptors and the read and write
calls to pass information to one another. If the consumer calls the blocking
read system call before the producer has produced anything, the call will
block the event queue (while executing the system call instruction) and
deadlock the simulation.

The solution implemented in this changeset is to recognize that the system
calls will block and then generate a special retry fault. The fault will
be sent back up through the function call chain until it is exposed to the
cpu model's pipeline where the fault becomes visible. The fault will trigger
the cpu model to replay the instruction at a future tick where the call has
a chance to succeed without actually going into a blocking state.

In subsequent patches, we recognize that a syscall will block by calling a
non-blocking poll (from inside the system call implementation) and checking
for events. When events show up during the poll, it signifies that the call
would not have blocked and the syscall is allowed to proceed (calling an
underlying host system call if necessary). If no events are returned from the
poll, we generate the fault and try the instruction for the thread context
at a distant tick. Note that retrying every tick is not efficient.

As an aside, the simulator has some multi-threading support for the event
queue, but it is not used by default and needs work. Even if the event queue
was completely multi-threaded, meaning that there is a hardware thread on
the host servicing a single simulator thread contexts with a 1:1 mapping
between them, it's still possible to run into deadlock due to the event queue
barriers on quantum boundaries. The solution of replaying at a later tick
is the simplest solution and solves the problem generally.
2015-07-20 09:15:21 -05:00

362 lines
10 KiB
C++

/*
* Copyright (c) 2011-2014 ARM Limited
* Copyright (c) 2013 Advanced Micro Devices, Inc.
* All rights reserved
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Copyright (c) 2002-2005 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Steve Reinhardt
* Dave Greene
* Nathan Binkert
* Andrew Bardsley
*/
/**
* @file
*
* ExecContext bears the exec_context interface for Minor.
*/
#ifndef __CPU_MINOR_EXEC_CONTEXT_HH__
#define __CPU_MINOR_EXEC_CONTEXT_HH__
#include "cpu/exec_context.hh"
#include "cpu/minor/execute.hh"
#include "cpu/minor/pipeline.hh"
#include "cpu/base.hh"
#include "cpu/simple_thread.hh"
#include "mem/request.hh"
#include "debug/MinorExecute.hh"
namespace Minor
{
/* Forward declaration of Execute */
class Execute;
/** ExecContext bears the exec_context interface for Minor. This nicely
* separates that interface from other classes such as Pipeline, MinorCPU
* and DynMinorInst and makes it easier to see what state is accessed by it.
*/
class ExecContext : public ::ExecContext
{
public:
MinorCPU &cpu;
/** ThreadState object, provides all the architectural state. */
SimpleThread &thread;
/** The execute stage so we can peek at its contents. */
Execute &execute;
/** Instruction for the benefit of memory operations and for PC */
MinorDynInstPtr inst;
ExecContext (
MinorCPU &cpu_,
SimpleThread &thread_, Execute &execute_,
MinorDynInstPtr inst_) :
cpu(cpu_),
thread(thread_),
execute(execute_),
inst(inst_)
{
DPRINTF(MinorExecute, "ExecContext setting PC: %s\n", inst->pc);
pcState(inst->pc);
setPredicate(true);
thread.setIntReg(TheISA::ZeroReg, 0);
#if THE_ISA == ALPHA_ISA
thread.setFloatReg(TheISA::ZeroReg, 0.0);
#endif
}
Fault
initiateMemRead(Addr addr, unsigned int size,
Request::Flags flags) override
{
execute.getLSQ().pushRequest(inst, true /* load */, nullptr,
size, addr, flags, NULL);
return NoFault;
}
Fault
writeMem(uint8_t *data, unsigned int size, Addr addr,
Request::Flags flags, uint64_t *res) override
{
execute.getLSQ().pushRequest(inst, false /* store */, data,
size, addr, flags, res);
return NoFault;
}
IntReg
readIntRegOperand(const StaticInst *si, int idx) override
{
return thread.readIntReg(si->srcRegIdx(idx));
}
TheISA::FloatReg
readFloatRegOperand(const StaticInst *si, int idx) override
{
int reg_idx = si->srcRegIdx(idx) - TheISA::FP_Reg_Base;
return thread.readFloatReg(reg_idx);
}
TheISA::FloatRegBits
readFloatRegOperandBits(const StaticInst *si, int idx) override
{
int reg_idx = si->srcRegIdx(idx) - TheISA::FP_Reg_Base;
return thread.readFloatRegBits(reg_idx);
}
void
setIntRegOperand(const StaticInst *si, int idx, IntReg val) override
{
thread.setIntReg(si->destRegIdx(idx), val);
}
void
setFloatRegOperand(const StaticInst *si, int idx,
TheISA::FloatReg val) override
{
int reg_idx = si->destRegIdx(idx) - TheISA::FP_Reg_Base;
thread.setFloatReg(reg_idx, val);
}
void
setFloatRegOperandBits(const StaticInst *si, int idx,
TheISA::FloatRegBits val) override
{
int reg_idx = si->destRegIdx(idx) - TheISA::FP_Reg_Base;
thread.setFloatRegBits(reg_idx, val);
}
bool
readPredicate() override
{
return thread.readPredicate();
}
void
setPredicate(bool val) override
{
thread.setPredicate(val);
}
TheISA::PCState
pcState() const override
{
return thread.pcState();
}
void
pcState(const TheISA::PCState &val) override
{
thread.pcState(val);
}
TheISA::MiscReg
readMiscRegNoEffect(int misc_reg) const
{
return thread.readMiscRegNoEffect(misc_reg);
}
TheISA::MiscReg
readMiscReg(int misc_reg) override
{
return thread.readMiscReg(misc_reg);
}
void
setMiscReg(int misc_reg, const TheISA::MiscReg &val) override
{
thread.setMiscReg(misc_reg, val);
}
TheISA::MiscReg
readMiscRegOperand(const StaticInst *si, int idx) override
{
int reg_idx = si->srcRegIdx(idx) - TheISA::Misc_Reg_Base;
return thread.readMiscReg(reg_idx);
}
void
setMiscRegOperand(const StaticInst *si, int idx,
const TheISA::MiscReg &val) override
{
int reg_idx = si->destRegIdx(idx) - TheISA::Misc_Reg_Base;
return thread.setMiscReg(reg_idx, val);
}
Fault
hwrei() override
{
#if THE_ISA == ALPHA_ISA
return thread.hwrei();
#else
return NoFault;
#endif
}
bool
simPalCheck(int palFunc) override
{
#if THE_ISA == ALPHA_ISA
return thread.simPalCheck(palFunc);
#else
return false;
#endif
}
void
syscall(int64_t callnum, Fault *fault) override
{
if (FullSystem)
panic("Syscall emulation isn't available in FS mode.\n");
thread.syscall(callnum, fault);
}
ThreadContext *tcBase() override { return thread.getTC(); }
/* @todo, should make stCondFailures persistent somewhere */
unsigned int readStCondFailures() const override { return 0; }
void setStCondFailures(unsigned int st_cond_failures) override {}
ContextID contextId() { return thread.contextId(); }
/* ISA-specific (or at least currently ISA singleton) functions */
/* X86: TLB twiddling */
void
demapPage(Addr vaddr, uint64_t asn) override
{
thread.getITBPtr()->demapPage(vaddr, asn);
thread.getDTBPtr()->demapPage(vaddr, asn);
}
TheISA::CCReg
readCCRegOperand(const StaticInst *si, int idx) override
{
int reg_idx = si->srcRegIdx(idx) - TheISA::CC_Reg_Base;
return thread.readCCReg(reg_idx);
}
void
setCCRegOperand(const StaticInst *si, int idx, TheISA::CCReg val) override
{
int reg_idx = si->destRegIdx(idx) - TheISA::CC_Reg_Base;
thread.setCCReg(reg_idx, val);
}
void
demapInstPage(Addr vaddr, uint64_t asn)
{
thread.getITBPtr()->demapPage(vaddr, asn);
}
void
demapDataPage(Addr vaddr, uint64_t asn)
{
thread.getDTBPtr()->demapPage(vaddr, asn);
}
/* ALPHA/POWER: Effective address storage */
void setEA(Addr ea) override
{
inst->ea = ea;
}
BaseCPU *getCpuPtr() { return &cpu; }
/* POWER: Effective address storage */
Addr getEA() const override
{
return inst->ea;
}
/* MIPS: other thread register reading/writing */
uint64_t
readRegOtherThread(int idx, ThreadID tid = InvalidThreadID)
{
SimpleThread *other_thread = (tid == InvalidThreadID
? &thread : cpu.threads[tid]);
if (idx < TheISA::FP_Reg_Base) { /* Integer */
return other_thread->readIntReg(idx);
} else if (idx < TheISA::Misc_Reg_Base) { /* Float */
return other_thread->readFloatRegBits(idx
- TheISA::FP_Reg_Base);
} else { /* Misc */
return other_thread->readMiscReg(idx
- TheISA::Misc_Reg_Base);
}
}
void
setRegOtherThread(int idx, const TheISA::MiscReg &val,
ThreadID tid = InvalidThreadID)
{
SimpleThread *other_thread = (tid == InvalidThreadID
? &thread : cpu.threads[tid]);
if (idx < TheISA::FP_Reg_Base) { /* Integer */
return other_thread->setIntReg(idx, val);
} else if (idx < TheISA::Misc_Reg_Base) { /* Float */
return other_thread->setFloatRegBits(idx
- TheISA::FP_Reg_Base, val);
} else { /* Misc */
return other_thread->setMiscReg(idx
- TheISA::Misc_Reg_Base, val);
}
}
public:
// monitor/mwait funtions
void armMonitor(Addr address) override
{ getCpuPtr()->armMonitor(inst->id.threadId, address); }
bool mwait(PacketPtr pkt) override
{ return getCpuPtr()->mwait(inst->id.threadId, pkt); }
void mwaitAtomic(ThreadContext *tc) override
{ return getCpuPtr()->mwaitAtomic(inst->id.threadId, tc, thread.dtb); }
AddressMonitor *getAddrMonitor() override
{ return getCpuPtr()->getCpuAddrMonitor(inst->id.threadId); }
};
}
#endif /* __CPU_MINOR_EXEC_CONTEXT_HH__ */