Re: [patch 3/4] QEMU/KVM: ignore SIG_IPI signals in userspace

[Marcelo Tosatti <mtosatti@redhat.com>]

On Sun, Apr 06, 2008 at 12:15:07PM +0300, Avi Kivity wrote:
> Marcelo Tosatti wrote:
> >Otherwise a signal can be received in userspace and a vcpu goes back
> >to the kernel while it should stay still.
> >
> >Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> >
> >Index: kvm-userspace.io/qemu/qemu-kvm.c
> >===================================================================
> >--- kvm-userspace.io.orig/qemu/qemu-kvm.c
> >+++ kvm-userspace.io/qemu/qemu-kvm.c
> >@@ -350,7 +350,6 @@ static void *ap_main_loop(void *_env)
> >     vcpu->env = env;
> >     vcpu->env->thread_id = kvm_get_thread_id();
> >     sigfillset(&signals);
> >-    sigdelset(&signals, SIG_IPI);
> >     sigprocmask(SIG_BLOCK, &signals, NULL);
> >     kvm_create_vcpu(kvm_context, env->cpu_index);
> >     kvm_qemu_init_env(env);
> >
> >  
> 
> Does this work with -no-kvm-irqchip?

Yes. SIG_IPI was blocked before the IO thread.

> I think we need to fix the kernel to handle random signals.  Otherwise 
> even attaching a debugger can change guest behavior (I think).

Well ptrace forces signals so SIGSTOP is delivered even though the child
has blocked them.

Attaching a debugger does change behaviour since SIGSTOP will send a
vcpu back to userspace.

Can you be more specific?


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