jcs.org
qemu with hax to log dma reads & writes
jcs.org/2018/11/12/vfio
membarrier: introduce qemu/sys_membarrier.h
This new header file provides heavy-weight "global" memory barriers that
enforce memory ordering on each running thread belonging to the current
process. For now, use a dummy implementation that issues memory barriers
on both sides (matching what QEMU has been doing so far).
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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include/qemu/rcu.h
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include/qemu/rcu.h
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#include "qemu/thread.h"
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#include "qemu/queue.h"
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#include "qemu/atomic.h"
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#include "qemu/sys_membarrier.h"
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#ifdef __cplusplus
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extern "C" {
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atomic_set(&p_rcu_reader->ctr, ctr);
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/* Write p_rcu_reader->ctr before reading RCU-protected pointers. */
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smp_mb();
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smp_mb_placeholder();
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}
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static inline void rcu_read_unlock(void)
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/* Ensure that the critical section is seen to precede the
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* store to p_rcu_reader->ctr. Together with the following
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* smp_mb(), this ensures writes to p_rcu_reader->ctr
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* smp_mb_placeholder(), this ensures writes to p_rcu_reader->ctr
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* are sequentially consistent.
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*/
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atomic_store_release(&p_rcu_reader->ctr, 0);
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/* Write p_rcu_reader->ctr before reading p_rcu_reader->waiting. */
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smp_mb();
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smp_mb_placeholder();
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if (unlikely(atomic_read(&p_rcu_reader->waiting))) {
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atomic_set(&p_rcu_reader->waiting, false);
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qemu_event_set(&rcu_gp_event);
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include/qemu/sys_membarrier.h
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include/qemu/sys_membarrier.h
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/*
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* Process-global memory barriers
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*
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* Copyright (c) 2018 Red Hat, Inc.
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*
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* Author: Paolo Bonzini <pbonzini@redhat.com>
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*/
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#ifndef QEMU_SYS_MEMBARRIER_H
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#define QEMU_SYS_MEMBARRIER_H 1
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/* Keep it simple, execute a real memory barrier on both sides. */
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static inline void smp_mb_global_init(void) {}
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#define smp_mb_global() smp_mb()
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#define smp_mb_placeholder() smp_mb()
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#endif
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util/rcu.c
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util/rcu.c
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}
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/* Here, order the stores to index->waiting before the loads of
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* index->ctr. Pairs with smp_mb() in rcu_read_unlock(),
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* index->ctr. Pairs with smp_mb_placeholder() in rcu_read_unlock(),
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* ensuring that the loads of index->ctr are sequentially consistent.
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*/
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smp_mb();
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smp_mb_global();
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QLIST_FOREACH_SAFE(index, ®istry, node, tmp) {
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if (!rcu_gp_ongoing(&index->ctr)) {
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qemu_mutex_lock(&rcu_sync_lock);
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/* Write RCU-protected pointers before reading p_rcu_reader->ctr.
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* Pairs with smp_mb() in rcu_read_lock().
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* Pairs with smp_mb_placeholder() in rcu_read_lock().
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*/
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smp_mb();
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smp_mb_global();
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qemu_mutex_lock(&rcu_registry_lock);
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if (!QLIST_EMPTY(®istry)) {
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static void __attribute__((__constructor__)) rcu_init(void)
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{
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smp_mb_global_init();
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#ifdef CONFIG_POSIX
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pthread_atfork(rcu_init_lock, rcu_init_unlock, rcu_init_child);
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#endif