Re: [Xen-devel] [PATCH v4 4/8] monitor: ARM SMC events

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Mon, Jul 4, 2016 at 2:02 PM, Julien Grall <julien.grall@xxxxxxx> wrote:
>
>
> On 04/07/2016 20:13, Tamas K Lengyel wrote:
>>>
>>> On ARMv8, ESR_EL2.ISS has a different encoding depending on the state
>>> (i.e
>>> AArch64 or AArch32). See D7-1861 in ARM DDI 0487A.i. Furthermore, in
>>> AArch32
>>> state, the ARMv8 specs permits to trap conditional SMC instructions that
>>> fail their condition check (see D7-1897 in ARM DDI 0406C.c).
>>
>>
>> Hi Julien,
>
>
> Hello Tamas,
>
>> I'm unable to find the reference you mention about conditional SMCs
>> generating Hyp traps even if they fail their condition checks on
>> certain implementations. The only references I find in ARMv8 manual
>> states explicitly that "The trap that HCR_EL2.TSC enables traps the
>> attempted execution of a conditional SMC instruction only if the
>> instruction passes its condition code check" (D1.15) and "The
>> architecture requires that a Hyp trap on a conditional SMC instruction
>> generates an exception only if the instruction passes its condition
>> code check, see Trapping use of the SMC instruction on page G1-3510"
>> (G1.16).
>
>
> If you look at description of HCR_EL2.TSC at D7-1973 in DDI 0487A.j;
> "In AArch32 state, the ARMv8-A architecture permits, but does not require,
> this trap to apply to conditional SMC instructions that fail their condition
> code check, in the same way as with traps on
> other conditional instructions."
>
> AFAICT the change was already present in the ARM ARM beginning of 2015. So I
> suspect you are using an old version of the spec. In general, I would
> recommend you to use the most recent spec for your development.
>
> For future question related to the spec, please mention the version of the
> spec you quote. It makes easier to find out what is going on.

Ah yes, indeed, I was looking at an older version. From the manual
though it is not clear to me how we can differentiate SMCs that had
their condition check fail from the others once its trapped to the
VMM.. Are you still planning to implement that filter?

Thanks,
Tamas

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