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afd46fcad2
In icount mode, instructions that access io memory spaces in the middle
of the translation block invoke TB recompilation. After recompilation,
such instructions become last in the TB and are allowed to access io
memory spaces.
When the code includes instruction like i386 'xchg eax, 0xffffd080'
which accesses APIC, QEMU goes into an infinite loop of the recompilation.
This instruction includes two memory accesses - one read and one write.
After the first access, APIC calls cpu_report_tpr_access, which restores
the CPU state to get the current eip. But cpu_restore_state_from_tb
resets the cpu->can_do_io flag which makes the second memory access invalid.
Therefore the second memory access causes a recompilation of the block.
Then these operations repeat again and again.
This patch moves resetting cpu->can_do_io flag from
cpu_restore_state_from_tb to cpu_loop_exit* functions.
It also adds a parameter for cpu_restore_state which controls restoring
icount. There is no need to restore icount when we only query CPU state
without breaking the TB. Restoring it in such cases leads to the
incorrect flow of the virtual time.
In most cases new parameter is true (icount should be recalculated).
But there are two cases in i386 and openrisc when the CPU state is only
queried without the need to break the TB. This patch fixes both of
these cases.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Message-Id: <20180409091320.12504.35329.stgit@pasha-VirtualBox>
[rth: Make can_do_io setting unconditional; move from cpu_exec;
make cpu_loop_exit_{noexc,restore} call cpu_loop_exit.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
84 lines
2.8 KiB
C
84 lines
2.8 KiB
C
/*
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* emulator main execution loop
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*
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* Copyright (c) 2003-2005 Fabrice Bellard
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include "qemu/osdep.h"
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#include "cpu.h"
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#include "sysemu/cpus.h"
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#include "exec/exec-all.h"
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bool tcg_allowed;
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/* exit the current TB, but without causing any exception to be raised */
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void cpu_loop_exit_noexc(CPUState *cpu)
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{
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cpu->exception_index = -1;
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cpu_loop_exit(cpu);
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}
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#if defined(CONFIG_SOFTMMU)
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void cpu_reloading_memory_map(void)
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{
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if (qemu_in_vcpu_thread() && current_cpu->running) {
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/* The guest can in theory prolong the RCU critical section as long
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* as it feels like. The major problem with this is that because it
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* can do multiple reconfigurations of the memory map within the
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* critical section, we could potentially accumulate an unbounded
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* collection of memory data structures awaiting reclamation.
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*
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* Because the only thing we're currently protecting with RCU is the
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* memory data structures, it's sufficient to break the critical section
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* in this callback, which we know will get called every time the
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* memory map is rearranged.
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*
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* (If we add anything else in the system that uses RCU to protect
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* its data structures, we will need to implement some other mechanism
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* to force TCG CPUs to exit the critical section, at which point this
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* part of this callback might become unnecessary.)
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*
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* This pair matches cpu_exec's rcu_read_lock()/rcu_read_unlock(), which
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* only protects cpu->as->dispatch. Since we know our caller is about
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* to reload it, it's safe to split the critical section.
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*/
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rcu_read_unlock();
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rcu_read_lock();
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}
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}
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#endif
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void cpu_loop_exit(CPUState *cpu)
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{
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/* Undo the setting in cpu_tb_exec. */
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cpu->can_do_io = 1;
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siglongjmp(cpu->jmp_env, 1);
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}
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void cpu_loop_exit_restore(CPUState *cpu, uintptr_t pc)
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{
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if (pc) {
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cpu_restore_state(cpu, pc, true);
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}
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cpu_loop_exit(cpu);
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}
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void cpu_loop_exit_atomic(CPUState *cpu, uintptr_t pc)
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{
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cpu->exception_index = EXCP_ATOMIC;
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cpu_loop_exit_restore(cpu, pc);
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}
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