Re: [Xen-devel] [PATCH v3] Fix the mistake of exception execution

[Aravindh Puthiyaparambil <aravindh@xxxxxxxxxxxx>]

On Mon, May 14, 2012 at 11:48 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>
> >>> On 15.05.12 at 07:59, "Hao, Xudong" <xudong.hao@xxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> >>> On 14.05.12 at 12:41, "Hao, Xudong" <xudong.hao@xxxxxxxxx> wrote:
> >> >      default:
> >> > -        if ( trap > TRAP_last_reserved )
> >> > -        {
> >> > -            type = X86_EVENTTYPE_SW_EXCEPTION;
> >> > -            __vmwrite(VM_ENTRY_INSTRUCTION_LEN, 2); /* int imm8 */
> >> > -        }
> >>
> >> So this undoes Aravindh's earlier change, without replacement. I
> >> don't think that's acceptable.
> >>
> >
> > This is the first patch that just correct some instruction in hw exception
> > function, as function description above, int n (n > 32) is not delivered by
> > this function.
> > I'll write another patch of new function for int n handler.
>
> In that case it would have been nice to indicate that you don't expect
> this to be applied just yet (i.e. by marking the patch RFC).
>
> >> > +                    __vmwrite(VM_ENTRY_INSTRUCTION_LEN, 1); /* int3, CC 
> >> > */
> >>
> >> Still using a hard-coded 1 here, the more that afaict you can't
> >> distinguish CC and CD 03 here.
> >>
> >
> > Just copied it from original code, how about this replacement:
> >
> > +     __vmwrite(VM_ENTRY_INSTRUCTION_LEN, 
> > __vmread(VM_EXIT_INSTRUCTION_LEN));
>
> That's okay as long as on all possible code paths arriving here
> VM_EXIT_INSTRUCTION_LEN is actually valid. I'm suspicious this might
> not be the case (especially in the case of injection originating from
> libxc).

Your suspicion is warranted. IIRC this did not work for the libxc case
injecting software interrupts. That is why I hard coded the
instruction length. Maybe the instruction length can be made caller
specific?

Thanks,
Aravindh

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