Re: [Xen-devel] [PATCH v5 5/9] monitor: ARM SMC events

[Julien Grall <julien.grall@xxxxxxx>]

Hello Tamas,

On 06/06/16 16:24, Tamas K Lengyel wrote:
> On Jun 6, 2016 04:08, "Julien Grall" <julien.grall@xxxxxxx
> <mailto:julien.grall@xxxxxxx>> wrote:
>  >
>  > Hello,
>  >
>  >
>  > On 04/06/2016 18:40, Tamas K Lengyel wrote:
>  >>
>  >> On Sat, Jun 4, 2016 at 3:03 AM, Edgar E. Iglesias
>  >> <edgar.iglesias@xxxxxxxxx <mailto:edgar.iglesias@xxxxxxxxx>> wrote:
>  >>>
>  >>> Forwarding SMC events for SMC insns that didn't pass the condition
> tests
>  >>> doesn't make any sense to me. It'll just make the receivers job harder.
>  >>> Why would a receiver want to do anything else than drop these?
>  >>> If it actually does look at them it'll be looking at implementation
>  >>> defined HW behaviour that may vary between CPU implementations.
>  >>
>  >>
>  >> If for no other purposes it may be useful to log them to be able to
>  >> study the CPU implementation's behavior.
>  >
>  >
>  > I cannot see how you will be able to study ARM CPU implementation's
> behavior with VM event. Though I am not familiar with it.
>  >
>  > For now, it looks like to me that forwarding conditional SMC even if
> the condition check has failed will require a lot of code in each
> introspection applications, not to mention that they will need specific
> code to distinguish ARMv7 vs ARMv8.
>
> Why would it require any more code? Right now the only thing the
> listener can do is to increment pc to jump over the SMC. That would be
> the same regardless of what type it was. As for checking whether it was
> v7 or v8, if that is of interest to the app it should implement the
> appropriate logic for it. I don't see a problem there either.
A listener can to do more then incrementing pc to jump over the SMC. The 
app may want to decode the instruction to get the immediate and then 
execute different actions depending on its value (for instance to 
emulate some SMC call).
For this kind of app, it will be necessary to find out whether the 
condition check has failed or not before executing it.
Regards,

--
Julien Grall

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