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author | Emanuele Giuseppe Esposito <eesposit@redhat.com> | 2022-11-11 10:47:56 -0500 |
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committer | Paolo Bonzini <pbonzini@redhat.com> | 2023-01-11 09:59:39 +0100 |
commit | bd688fc93120fb3e28aa70e3dfdf567ccc1e0bc1 (patch) | |
tree | d763c7b30c195a31dedf67d708b7d770fd16b5ef | |
parent | b585edca34a817fdb751dfe94fbd3cde32ffe60d (diff) | |
download | qemu-bd688fc93120fb3e28aa70e3dfdf567ccc1e0bc1.zip qemu-bd688fc93120fb3e28aa70e3dfdf567ccc1e0bc1.tar.gz qemu-bd688fc93120fb3e28aa70e3dfdf567ccc1e0bc1.tar.bz2 |
accel: introduce accelerator blocker API
This API allows the accelerators to prevent vcpus from issuing
new ioctls while execting a critical section marked with the
accel_ioctl_inhibit_begin/end functions.
Note that all functions submitting ioctls must mark where the
ioctl is being called with accel_{cpu_}ioctl_begin/end().
This API requires the caller to always hold the BQL.
API documentation is in sysemu/accel-blocker.h
Internally, it uses a QemuLockCnt together with a per-CPU QemuLockCnt
(to minimize cache line bouncing) to keep avoid that new ioctls
run when the critical section starts, and a QemuEvent to wait
that all running ioctls finish.
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20221111154758.1372674-2-eesposit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r-- | accel/accel-blocker.c | 154 | ||||
-rw-r--r-- | accel/meson.build | 2 | ||||
-rw-r--r-- | hw/core/cpu-common.c | 2 | ||||
-rw-r--r-- | include/hw/core/cpu.h | 3 | ||||
-rw-r--r-- | include/sysemu/accel-blocker.h | 56 | ||||
-rw-r--r-- | util/meson.build | 2 |
6 files changed, 217 insertions, 2 deletions
diff --git a/accel/accel-blocker.c b/accel/accel-blocker.c new file mode 100644 index 0000000..1e7f423 --- /dev/null +++ b/accel/accel-blocker.c @@ -0,0 +1,154 @@ +/* + * Lock to inhibit accelerator ioctls + * + * Copyright (c) 2022 Red Hat Inc. + * + * Author: Emanuele Giuseppe Esposito <eesposit@redhat.com> + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN + * THE SOFTWARE. + */ + +#include "qemu/osdep.h" +#include "qemu/thread.h" +#include "qemu/main-loop.h" +#include "hw/core/cpu.h" +#include "sysemu/accel-blocker.h" + +static QemuLockCnt accel_in_ioctl_lock; +static QemuEvent accel_in_ioctl_event; + +void accel_blocker_init(void) +{ + qemu_lockcnt_init(&accel_in_ioctl_lock); + qemu_event_init(&accel_in_ioctl_event, false); +} + +void accel_ioctl_begin(void) +{ + if (likely(qemu_mutex_iothread_locked())) { + return; + } + + /* block if lock is taken in kvm_ioctl_inhibit_begin() */ + qemu_lockcnt_inc(&accel_in_ioctl_lock); +} + +void accel_ioctl_end(void) +{ + if (likely(qemu_mutex_iothread_locked())) { + return; + } + + qemu_lockcnt_dec(&accel_in_ioctl_lock); + /* change event to SET. If event was BUSY, wake up all waiters */ + qemu_event_set(&accel_in_ioctl_event); +} + +void accel_cpu_ioctl_begin(CPUState *cpu) +{ + if (unlikely(qemu_mutex_iothread_locked())) { + return; + } + + /* block if lock is taken in kvm_ioctl_inhibit_begin() */ + qemu_lockcnt_inc(&cpu->in_ioctl_lock); +} + +void accel_cpu_ioctl_end(CPUState *cpu) +{ + if (unlikely(qemu_mutex_iothread_locked())) { + return; + } + + qemu_lockcnt_dec(&cpu->in_ioctl_lock); + /* change event to SET. If event was BUSY, wake up all waiters */ + qemu_event_set(&accel_in_ioctl_event); +} + +static bool accel_has_to_wait(void) +{ + CPUState *cpu; + bool needs_to_wait = false; + + CPU_FOREACH(cpu) { + if (qemu_lockcnt_count(&cpu->in_ioctl_lock)) { + /* exit the ioctl, if vcpu is running it */ + qemu_cpu_kick(cpu); + needs_to_wait = true; + } + } + + return needs_to_wait || qemu_lockcnt_count(&accel_in_ioctl_lock); +} + +void accel_ioctl_inhibit_begin(void) +{ + CPUState *cpu; + + /* + * We allow to inhibit only when holding the BQL, so we can identify + * when an inhibitor wants to issue an ioctl easily. + */ + g_assert(qemu_mutex_iothread_locked()); + + /* Block further invocations of the ioctls outside the BQL. */ + CPU_FOREACH(cpu) { + qemu_lockcnt_lock(&cpu->in_ioctl_lock); + } + qemu_lockcnt_lock(&accel_in_ioctl_lock); + + /* Keep waiting until there are running ioctls */ + while (true) { + + /* Reset event to FREE. */ + qemu_event_reset(&accel_in_ioctl_event); + + if (accel_has_to_wait()) { + /* + * If event is still FREE, and there are ioctls still in progress, + * wait. + * + * If an ioctl finishes before qemu_event_wait(), it will change + * the event state to SET. This will prevent qemu_event_wait() from + * blocking, but it's not a problem because if other ioctls are + * still running the loop will iterate once more and reset the event + * status to FREE so that it can wait properly. + * + * If an ioctls finishes while qemu_event_wait() is blocking, then + * it will be waken up, but also here the while loop makes sure + * to re-enter the wait if there are other running ioctls. + */ + qemu_event_wait(&accel_in_ioctl_event); + } else { + /* No ioctl is running */ + return; + } + } +} + +void accel_ioctl_inhibit_end(void) +{ + CPUState *cpu; + + qemu_lockcnt_unlock(&accel_in_ioctl_lock); + CPU_FOREACH(cpu) { + qemu_lockcnt_unlock(&cpu->in_ioctl_lock); + } +} + diff --git a/accel/meson.build b/accel/meson.build index 3a480cc..49558dd 100644 --- a/accel/meson.build +++ b/accel/meson.build @@ -1,4 +1,4 @@ -specific_ss.add(files('accel-common.c')) +specific_ss.add(files('accel-common.c', 'accel-blocker.c')) softmmu_ss.add(files('accel-softmmu.c')) user_ss.add(files('accel-user.c')) diff --git a/hw/core/cpu-common.c b/hw/core/cpu-common.c index b177e76..5ccc383 100644 --- a/hw/core/cpu-common.c +++ b/hw/core/cpu-common.c @@ -238,6 +238,7 @@ static void cpu_common_initfn(Object *obj) cpu->cflags_next_tb = -1; qemu_mutex_init(&cpu->work_mutex); + qemu_lockcnt_init(&cpu->in_ioctl_lock); QSIMPLEQ_INIT(&cpu->work_list); QTAILQ_INIT(&cpu->breakpoints); QTAILQ_INIT(&cpu->watchpoints); @@ -249,6 +250,7 @@ static void cpu_common_finalize(Object *obj) { CPUState *cpu = CPU(obj); + qemu_lockcnt_destroy(&cpu->in_ioctl_lock); qemu_mutex_destroy(&cpu->work_mutex); } diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h index 8830546..2417597 100644 --- a/include/hw/core/cpu.h +++ b/include/hw/core/cpu.h @@ -398,6 +398,9 @@ struct CPUState { uint32_t kvm_fetch_index; uint64_t dirty_pages; + /* Use by accel-block: CPU is executing an ioctl() */ + QemuLockCnt in_ioctl_lock; + /* Used for events with 'vcpu' and *without* the 'disabled' properties */ DECLARE_BITMAP(trace_dstate_delayed, CPU_TRACE_DSTATE_MAX_EVENTS); DECLARE_BITMAP(trace_dstate, CPU_TRACE_DSTATE_MAX_EVENTS); diff --git a/include/sysemu/accel-blocker.h b/include/sysemu/accel-blocker.h new file mode 100644 index 0000000..7202052 --- /dev/null +++ b/include/sysemu/accel-blocker.h @@ -0,0 +1,56 @@ +/* + * Accelerator blocking API, to prevent new ioctls from starting and wait the + * running ones finish. + * This mechanism differs from pause/resume_all_vcpus() in that it does not + * release the BQL. + * + * Copyright (c) 2022 Red Hat Inc. + * + * Author: Emanuele Giuseppe Esposito <eesposit@redhat.com> + * + * This work is licensed under the terms of the GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + */ +#ifndef ACCEL_BLOCKER_H +#define ACCEL_BLOCKER_H + +#include "qemu/osdep.h" +#include "sysemu/cpus.h" + +extern void accel_blocker_init(void); + +/* + * accel_{cpu_}ioctl_begin/end: + * Mark when ioctl is about to run or just finished. + * + * accel_{cpu_}ioctl_begin will block after accel_ioctl_inhibit_begin() is + * called, preventing new ioctls to run. They will continue only after + * accel_ioctl_inibith_end(). + */ +extern void accel_ioctl_begin(void); +extern void accel_ioctl_end(void); +extern void accel_cpu_ioctl_begin(CPUState *cpu); +extern void accel_cpu_ioctl_end(CPUState *cpu); + +/* + * accel_ioctl_inhibit_begin: start critical section + * + * This function makes sure that: + * 1) incoming accel_{cpu_}ioctl_begin() calls block + * 2) wait that all ioctls that were already running reach + * accel_{cpu_}ioctl_end(), kicking vcpus if necessary. + * + * This allows the caller to access shared data or perform operations without + * worrying of concurrent vcpus accesses. + */ +extern void accel_ioctl_inhibit_begin(void); + +/* + * accel_ioctl_inhibit_end: end critical section started by + * accel_ioctl_inhibit_begin() + * + * This function allows blocked accel_{cpu_}ioctl_begin() to continue. + */ +extern void accel_ioctl_inhibit_end(void); + +#endif /* ACCEL_BLOCKER_H */ diff --git a/util/meson.build b/util/meson.build index d8d109f..26c73e5 100644 --- a/util/meson.build +++ b/util/meson.build @@ -58,6 +58,7 @@ util_ss.add(files('yank.c')) util_ss.add(files('int128.c')) util_ss.add(files('memalign.c')) util_ss.add(files('interval-tree.c')) +util_ss.add(files('lockcnt.c')) if have_user util_ss.add(files('selfmap.c')) @@ -72,7 +73,6 @@ endif if have_block or have_ga util_ss.add(files('aiocb.c', 'async.c')) util_ss.add(files('base64.c')) - util_ss.add(files('lockcnt.c')) util_ss.add(files('main-loop.c')) util_ss.add(files('qemu-coroutine.c', 'qemu-coroutine-lock.c', 'qemu-coroutine-io.c')) util_ss.add(files('coroutine-@0@.c'.format(config_host['CONFIG_COROUTINE_BACKEND']))) |