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exec: RCUify AddressSpaceDispatch

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Note that even after this patch, most callers of address_space_*
functions must still be under the big QEMU lock, otherwise the memory
region returned by address_space_translate can disappear as soon as
address_space_translate returns.  This will be fixed in the next part
of this series.

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2015-01-21 12:09:14 +01:00
parent 9d82b5a792
commit 79e2b9aecc
8 changed files with 63 additions and 12 deletions
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25
cpu-exec.c
View file

@ -26,6 +26,7 @@
#include "qemu/timer.h"
#include "exec/address-spaces.h"
#include "exec/memory-internal.h"
#include "qemu/rcu.h"
/* -icount align implementation. */
@ -146,8 +147,27 @@ void cpu_resume_from_signal(CPUState *cpu, void *puc)
void cpu_reload_memory_map(CPUState *cpu)
{
AddressSpaceDispatch *d;
if (qemu_in_vcpu_thread()) {
/* Do not let the guest prolong the critical section as much as it
* as it desires.
*
* Currently, this is prevented by the I/O thread's periodinc kicking
* of the VCPU thread (iothread_requesting_mutex, qemu_cpu_kick_thread)
* but this will go away once TCG's execution moves out of the global
* mutex.
*
* 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. */
AddressSpaceDispatch *d = cpu->as->dispatch;
d = atomic_rcu_read(&cpu->as->dispatch);
cpu->memory_dispatch = d;
tlb_flush(cpu, 1);
}
@ -362,6 +382,8 @@ int cpu_exec(CPUArchState *env)
* an instruction scheduling constraint on modern architectures. */
smp_mb();
rcu_read_lock();
if (unlikely(exit_request)) {
cpu->exit_request = 1;
}
@ -564,6 +586,7 @@ int cpu_exec(CPUArchState *env)
} /* for(;;) */
cc->cpu_exec_exit(cpu);
rcu_read_unlock();
/* fail safe : never use current_cpu outside cpu_exec() */
current_cpu = NULL;