From 79e2b9aeccedbfde762b05da662132c7fda292be Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 21 Jan 2015 12:09:14 +0100 Subject: exec: RCUify AddressSpaceDispatch 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 Signed-off-by: Paolo Bonzini --- cpu-exec.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) (limited to 'cpu-exec.c') diff --git a/cpu-exec.c b/cpu-exec.c index 98f968d..adb939a 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -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; -- cgit v1.1