mirror of
https://github.com/xemu-project/xemu.git
synced 2024-11-25 04:30:02 +00:00
53f8a5e9e2
The reason for cpu_reload_memory_map()'s RCU operations is not so much because the guest could make the critical section very long, but that it could have a critical section within which it made an arbitrary number of changes to the memory map and thus accumulate an unbounded amount of memory data structures awaiting reclamation. Clarify the comment to make this clearer. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Message-Id: <1443709790-25180-3-git-send-email-peter.maydell@linaro.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
90 lines
3.0 KiB
C
90 lines
3.0 KiB
C
/*
|
|
* emulator main execution loop
|
|
*
|
|
* Copyright (c) 2003-2005 Fabrice Bellard
|
|
*
|
|
* This library is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU Lesser General Public
|
|
* License as published by the Free Software Foundation; either
|
|
* version 2 of the License, or (at your option) any later version.
|
|
*
|
|
* This library is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
* Lesser General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU Lesser General Public
|
|
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#include "config.h"
|
|
#include "cpu.h"
|
|
#include "sysemu/cpus.h"
|
|
#include "exec/memory-internal.h"
|
|
|
|
bool exit_request;
|
|
CPUState *tcg_current_cpu;
|
|
|
|
/* exit the current TB from a signal handler. The host registers are
|
|
restored in a state compatible with the CPU emulator
|
|
*/
|
|
#if defined(CONFIG_SOFTMMU)
|
|
void cpu_resume_from_signal(CPUState *cpu, void *puc)
|
|
{
|
|
/* XXX: restore cpu registers saved in host registers */
|
|
|
|
cpu->exception_index = -1;
|
|
siglongjmp(cpu->jmp_env, 1);
|
|
}
|
|
|
|
void cpu_reload_memory_map(CPUState *cpu)
|
|
{
|
|
AddressSpaceDispatch *d;
|
|
|
|
if (qemu_in_vcpu_thread()) {
|
|
/* The guest can in theory prolong the RCU critical section as long
|
|
* as it feels like. The major problem with this is that because it
|
|
* can do multiple reconfigurations of the memory map within the
|
|
* critical section, we could potentially accumulate an unbounded
|
|
* collection of memory data structures awaiting reclamation.
|
|
*
|
|
* Because the only thing we're currently protecting with RCU is the
|
|
* memory data structures, it's sufficient to break the critical section
|
|
* in this callback, which we know will get called every time the
|
|
* memory map is rearranged.
|
|
*
|
|
* (If we add anything else in the system that uses RCU to protect
|
|
* its data structures, we will need to implement some other mechanism
|
|
* to force TCG CPUs to exit the critical section, at which point this
|
|
* part of this callback might become unnecessary.)
|
|
*
|
|
* This pair matches cpu_exec's rcu_read_lock()/rcu_read_unlock(), which
|
|
* only protects cpu->as->dispatch. Since we reload it below, we can
|
|
* split the critical section.
|
|
*/
|
|
rcu_read_unlock();
|
|
rcu_read_lock();
|
|
}
|
|
|
|
/* The CPU and TLB are protected by the iothread lock. */
|
|
d = atomic_rcu_read(&cpu->as->dispatch);
|
|
cpu->memory_dispatch = d;
|
|
tlb_flush(cpu, 1);
|
|
}
|
|
#endif
|
|
|
|
void cpu_loop_exit(CPUState *cpu)
|
|
{
|
|
cpu->current_tb = NULL;
|
|
siglongjmp(cpu->jmp_env, 1);
|
|
}
|
|
|
|
void cpu_loop_exit_restore(CPUState *cpu, uintptr_t pc)
|
|
{
|
|
if (pc) {
|
|
cpu_restore_state(cpu, pc);
|
|
}
|
|
cpu->current_tb = NULL;
|
|
siglongjmp(cpu->jmp_env, 1);
|
|
}
|