On Thu, Jan 27, 2011 at 02:09:58PM +0100, Jan Kiszka wrote:
> Found by Stefan Hajnoczi: There is a race in kvm_cpu_exec between
> checking for exit_request on vcpu entry and timer signals arriving
> before KVM starts to catch them. Plug it by blocking both timer related
> signals also on !CONFIG_IOTHREAD and process those via signalfd.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> CC: Stefan Hajnoczi <stefanha@xxxxxxxxxxxxxxxxxx>
> ---
> cpus.c | 18 ++++++++++++++++++
> 1 files changed, 18 insertions(+), 0 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index fc3f222..29b1070 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -254,6 +254,10 @@ static void qemu_kvm_init_cpu_signals(CPUState *env)
> pthread_sigmask(SIG_BLOCK, NULL, &set);
> sigdelset(&set, SIG_IPI);
> sigdelset(&set, SIGBUS);
> +#ifndef CONFIG_IOTHREAD
> + sigdelset(&set, SIGIO);
> + sigdelset(&set, SIGALRM);
> +#endif
I'd prefer separate qemu_kvm_init_cpu_signals in the !IOTHREAD
section.
> r = kvm_set_signal_mask(env, &set);
> if (r) {
> fprintf(stderr, "kvm_set_signal_mask: %s\n", strerror(-r));
> @@ -351,6 +355,12 @@ static void qemu_kvm_eat_signals(CPUState *env)
> exit(1);
> }
> } while (sigismember(&chkset, SIG_IPI) || sigismember(&chkset, SIGBUS));
> +
> +#ifndef CONFIG_IOTHREAD
> + if (sigismember(&chkset, SIGIO) || sigismember(&chkset, SIGALRM)) {
> + qemu_notify_event();
> + }
> +#endif
Why is this necessary?
You should break out of cpu_exec_all if there's a pending alarm (see
qemu_alarm_pending()).
> }
>
> #else /* _WIN32 */
> @@ -398,6 +408,14 @@ int qemu_init_main_loop(void)
> int ret;
>
> sigemptyset(&blocked_signals);
> + if (kvm_enabled()) {
> + /*
> + * We need to process timer signals synchronously to avoid a race
> + * between exit_request check and KVM vcpu entry.
> + */
> + sigaddset(&blocked_signals, SIGIO);
> + sigaddset(&blocked_signals, SIGALRM);
> + }
A block_io_signals() function for !IOTHREAD would be nicer.
>
> ret = qemu_signalfd_init(blocked_signals);
> if (ret) {
> --
> 1.7.1
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