Re: [Xen-devel] [PATCH] x86/vmx: Fix injection of #DB traps following XSA-156

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2016-01-05 at 06:53 +0000, Tian, Kevin wrote:
> > From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> > Sent: Monday, January 04, 2016 6:00 PM
> > 
> > Most #DB exceptions are traps rather than faults, meaning that the
> > instruction
> > pointer in the exception frame points after the instruction rather than
> > at it.
> > 
> > However, VMX intercepts all have fault semantics, even when
> > intercepting a
> > trap.ÂÂRe-injecting an intercepted trap as a fault causes an infinite
> > loop in
> > the guest, by re-executing the same trapping instruction
> > repeatedly.ÂÂThis
> > breaks debugging inside the guest.
> > 
> > Introduce a helper which copies VM_EXIT_INTR_INTO to
> > VM_ENTRY_INTR_INFO, and
> > use it to mirror the intercepted interrupt back to the guest.
> > 
> > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

Thanks. Andy tells me this issue is causing quite some havoc in the field
and we aren't sure when Jan is back from vacation so I have stepped outside
the usual scope of things I commit and applied this one. I hope that's OK
with everyone.

Ian.

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