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Date: Wed, 9 Oct 2013 23:11:39 -0300
From: Marcelo Tosatti <mtosatti@redhat.com>
Message-ID: <20131010021139.GB7060@amt.cnet>
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Subject: Re: [Qemu-devel] [patch 1/2] qemu: mempath: prefault pages manually
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org

On Wed, Oct 09, 2013 at 11:26:58PM +0200, Paolo Bonzini wrote:
> Il 09/10/2013 21:41, Marcelo Tosatti ha scritto:
> >> > How was that tested?  For BUS_MCEERR_AO it can work, but BUS_MCEERR_AR
> >> > calls force_sig_info which does this:
> >> > 
> >> >         ignored = action->sa.sa_handler == SIG_IGN;
> >> >         blocked = sigismember(&t->blocked, sig);
> >> >         if (blocked || ignored) {
> >> >                 action->sa.sa_handler = SIG_DFL;
> >> >                 if (blocked) {
> >> >                         sigdelset(&t->blocked, sig);
> >> >                         recalc_sigpending_and_wake(t);
> >> >                 }
> >> >         
> >> >         if (action->sa.sa_handler == SIG_DFL)
> >> >                 t->signal->flags &= ~SIGNAL_UNKILLABLE;
> >> > 
> >> > and kills the process (because that's the default action of SIG_DFL).
> > For vcpu context its not blocked?
> 
> It causes KVM to exit back to userspace, but as soon as KVM exits it
> should be blocked.  Thus a SIGBUS with BUS_MCEERR_AR will never be
> returned by sigtimedwait.

Its blocked but readable via signalfd.
Its generated when vcpu touches memory, see 77db5cbd29b7cb0e0fb4fd14.
Since its rarely used, reviewing the code is not a bad idea.

For the test, see
https://lists.nongnu.org/archive/html/qemu-devel/2011-01/msg01588.html.