RE: [Xen-devel] vmx_update_guest_cr() losing EXCEPTION_BITMAP setting

["Byrne, John (HP Labs)" <john.l.byrne@xxxxxx>]

The schedule_softirq() does close a hole I wasn't noticing.

Thanks.

> -----Original Message-----
> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
> Sent: Sunday, May 10, 2009 11:52 PM
> To: Byrne, John (HP Labs); xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] vmx_update_guest_cr() losing EXCEPTION_BITMAP
> setting
> 
> On 11/05/2009 05:32, "Byrne, John (HP Labs)" <john.l.byrne@xxxxxx>
> wrote:
> 
> > Running a heavily modified xen-unstable changset 19590:f80cf52a4fb6
> with
> > debugger_attached set, I was seeing the debug traps getting lost from
> the
> > EXCEPTION_BITMAP in vmx_update_guest_cr() when transitioning from
> real to
> > protected mode.  In my codebase, I could fix this trivially by
> clearing the
> > debug_state_latch and letting vmx_do_resume() reapply the setting.
> However,
> > while it looks like a valid issue in the unmodified codebase, I'm not
> sure. So
> > maybe someone might test/examine it and decide if it is real and
> whether some
> > more complex fix is required?
> 
> In vmx_update_guest_cr(), where EXCEPTION_BITMAP gets reset after exit
> from
> real mode, try setting v->arch.hvm_vcpu.debug_state_latch=0 and
> raise_softirq(SCHEDULE_SOFTIRQ).
> 
>  -- Keir
> 


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