unicorn/qemu/qom/cpu.c
Emilio G. Cota f66e74d65b
tcg: consistently access cpu->tb_jmp_cache atomically
Some code paths can lead to atomic accesses racing with memset()
on cpu->tb_jmp_cache, which can result in torn reads/writes
and is undefined behaviour in C11.

These torn accesses are unlikely to show up as bugs, but from code
inspection they seem possible. For example, tb_phys_invalidate does:
/* remove the TB from the hash list */
h = tb_jmp_cache_hash_func(tb->pc);
CPU_FOREACH(cpu) {
if (atomic_read(&cpu->tb_jmp_cache[h]) == tb) {
atomic_set(&cpu->tb_jmp_cache[h], NULL);
}
}
Here atomic_set might race with a concurrent memset (such as the
ones scheduled via "unsafe" async work, e.g. tlb_flush_page) and
therefore we might end up with a torn pointer (or who knows what,
because we are under undefined behaviour).

This patch converts parallel accesses to cpu->tb_jmp_cache to use
atomic primitives, thereby bringing these accesses back to defined
behaviour. The price to pay is to potentially execute more instructions
when clearing cpu->tb_jmp_cache, but given how infrequently they happen
and the small size of the cache, the performance impact I have measured
is within noise range when booting debian-arm.

Note that under "safe async" work (e.g. do_tb_flush) we could use memset
because no other vcpus are running. However I'm keeping these accesses
atomic as well to keep things simple and to avoid confusing analysis
tools such as ThreadSanitizer.

Backports commit f3ced3c59287dabc253f83f0c70aa4934470c15e from qemu
2018-03-03 21:12:36 -05:00

320 lines
7.7 KiB
C

/*
* QEMU CPU model
*
* Copyright (c) 2012-2014 SUSE LINUX Products GmbH
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see
* <http://www.gnu.org/licenses/gpl-2.0.html>
*/
#include "qemu/osdep.h"
#include "qapi/error.h"
#include "qemu-common.h"
#include "qemu/log.h"
#include "uc_priv.h"
bool cpu_exists(struct uc_struct* uc, int64_t id)
{
CPUState *cpu = uc->cpu;
CPUClass *cc = CPU_GET_CLASS(uc, cpu);
if (cc->get_arch_id(cpu) == id) {
return true;
}
return false;
}
CPUState *cpu_generic_init(struct uc_struct *uc, const char *typename, const char *cpu_model)
{
char *str, *name, *featurestr;
CPUState *cpu;
ObjectClass *oc;
CPUClass *cc;
Error *err = NULL;
str = g_strdup(cpu_model);
name = strtok(str, ",");
oc = cpu_class_by_name(uc, typename, name);
if (oc == NULL) {
g_free(str);
return NULL;
}
cpu = CPU(object_new(uc, object_class_get_name(oc)));
cc = CPU_GET_CLASS(uc, cpu);
featurestr = strtok(NULL, ",");
cc->parse_features(cpu, featurestr, &err);
g_free(str);
if (err != NULL) {
goto out;
}
object_property_set_bool(uc, OBJECT(cpu), true, "realized", &err);
out:
if (err != NULL) {
error_free(err);
object_unref(uc, OBJECT(cpu));
return NULL;
}
return cpu;
}
bool cpu_paging_enabled(const CPUState *cpu)
{
CPUClass *cc = CPU_GET_CLASS(cpu->uc, cpu);
return cc->get_paging_enabled(cpu);
}
static bool cpu_common_get_paging_enabled(const CPUState *cpu)
{
return false;
}
void cpu_get_memory_mapping(CPUState *cpu, MemoryMappingList *list,
Error **errp)
{
CPUClass *cc = CPU_GET_CLASS(cpu->uc, cpu);
cc->get_memory_mapping(cpu, list, errp);
}
static void cpu_common_get_memory_mapping(CPUState *cpu,
MemoryMappingList *list,
Error **errp)
{
error_setg(errp, "Obtaining memory mappings is unsupported on this CPU.");
}
void cpu_reset_interrupt(CPUState *cpu, int mask)
{
cpu->interrupt_request &= ~mask;
}
void cpu_exit(CPUState *cpu)
{
atomic_set(&cpu->exit_request, 1);
/* Ensure cpu_exec will see the exit request after TCG has exited. */
smp_wmb();
atomic_set(&cpu->tcg_exit_req, 1);
}
static void cpu_common_noop(CPUState *cpu)
{
}
static bool cpu_common_exec_interrupt(CPUState *cpu, int int_req)
{
return false;
}
void cpu_dump_state(CPUState *cpu, FILE *f, fprintf_function cpu_fprintf,
int flags)
{
CPUClass *cc = CPU_GET_CLASS(cpu->uc, cpu);
if (cc->dump_state) {
cc->dump_state(cpu, f, cpu_fprintf, flags);
}
}
void cpu_dump_statistics(CPUState *cpu, FILE *f, fprintf_function cpu_fprintf,
int flags)
{
CPUClass *cc = CPU_GET_CLASS(cpu->uc, cpu);
if (cc->dump_statistics) {
cc->dump_statistics(cpu, f, cpu_fprintf, flags);
}
}
void cpu_reset(CPUState *cpu)
{
CPUClass *klass = CPU_GET_CLASS(cpu->uc, cpu);
if (klass->reset != NULL) {
(*klass->reset)(cpu);
}
}
static void cpu_common_reset(CPUState *cpu)
{
CPUClass *cc = CPU_GET_CLASS(cpu->uc, cpu);
int i;
if (qemu_loglevel_mask(CPU_LOG_RESET)) {
qemu_log("CPU Reset (CPU %d)\n", cpu->cpu_index);
log_cpu_state(cpu, cc->reset_dump_flags);
}
cpu->interrupt_request = 0;
cpu->halted = 0;
cpu->mem_io_pc = 0;
cpu->mem_io_vaddr = 0;
cpu->icount_extra = 0;
cpu->icount_decr.u32 = 0;
cpu->can_do_io = 0;
cpu->exception_index = -1;
cpu->crash_occurred = false;
// TODO: Should be uncommented, but good 'ol
// unicorn's crappy symbol deduplication
// makes it impossible right now
//if (tcg_enabled(cpu->uc)) {
cpu_tb_jmp_cache_clear(cpu);
#ifdef CONFIG_SOFTMMU
tlb_flush(cpu);
#endif
//}
}
static bool cpu_common_has_work(CPUState *cs)
{
return false;
}
static bool cpu_common_debug_check_watchpoint(CPUState *cpu, CPUWatchpoint *wp)
{
/* If no extra check is required, QEMU watchpoint match can be considered
* as an architectural match.
*/
return true;
}
ObjectClass *cpu_class_by_name(struct uc_struct *uc, const char *typename, const char *cpu_model)
{
CPUClass *cc = CPU_CLASS(uc, object_class_by_name(uc, typename));
return cc->class_by_name(uc, cpu_model);
}
static ObjectClass *cpu_common_class_by_name(struct uc_struct *uc, const char *cpu_model)
{
return NULL;
}
static void cpu_common_parse_features(CPUState *cpu, char *features,
Error **errp)
{
char *featurestr; /* Single "key=value" string being parsed */
char *val;
Error *err = NULL;
featurestr = features ? strtok(features, ",") : NULL;
while (featurestr) {
val = strchr(featurestr, '=');
if (val) {
*val = 0;
val++;
object_property_parse(cpu->uc, OBJECT(cpu), val, featurestr, &err);
if (err) {
error_propagate(errp, err);
return;
}
} else {
error_setg(errp, "Expected key=value format, found %s.",
featurestr);
return;
}
featurestr = strtok(NULL, ",");
}
}
static int cpu_common_realizefn(struct uc_struct *uc, DeviceState *dev, Error **errp)
{
CPUState *cpu = CPU(dev);
if (dev->hotplugged) {
cpu_resume(cpu);
}
return 0;
}
static void cpu_common_initfn(struct uc_struct *uc, Object *obj, void *opaque)
{
CPUState *cpu = CPU(obj);
QTAILQ_INIT(&cpu->breakpoints);
QTAILQ_INIT(&cpu->watchpoints);
}
static int64_t cpu_common_get_arch_id(CPUState *cpu)
{
return cpu->cpu_index;
}
static vaddr cpu_adjust_watchpoint_address(CPUState *cpu, vaddr addr, int len)
{
return addr;
}
static void cpu_class_init(struct uc_struct *uc, ObjectClass *klass, void *data)
{
DeviceClass *dc = DEVICE_CLASS(uc, klass);
CPUClass *k = CPU_CLASS(uc, klass);
k->class_by_name = cpu_common_class_by_name;
k->parse_features = cpu_common_parse_features;
k->reset = cpu_common_reset;
k->get_arch_id = cpu_common_get_arch_id;
k->has_work = cpu_common_has_work;
k->get_paging_enabled = cpu_common_get_paging_enabled;
k->get_memory_mapping = cpu_common_get_memory_mapping;
k->debug_excp_handler = cpu_common_noop;
k->debug_check_watchpoint = cpu_common_debug_check_watchpoint;
k->cpu_exec_enter = cpu_common_noop;
k->cpu_exec_exit = cpu_common_noop;
k->cpu_exec_interrupt = cpu_common_exec_interrupt;
k->adjust_watchpoint_address = cpu_adjust_watchpoint_address;
dc->realize = cpu_common_realizefn;
/*
* Reason: CPUs still need special care by board code: wiring up
* IRQs, adding reset handlers, halting non-first CPUs, ...
*/
dc->cannot_instantiate_with_device_add_yet = true;
}
static const TypeInfo cpu_type_info = {
TYPE_CPU,
TYPE_DEVICE,
sizeof(CPUClass),
sizeof(CPUState),
NULL,
cpu_common_initfn,
NULL,
NULL,
NULL,
cpu_class_init,
NULL,
NULL,
true,
};
void cpu_register_types(struct uc_struct *uc)
{
type_register_static(uc, &cpu_type_info);
}