Re: [Xen-devel] [PATCH] xen: arm: fully implement multicall interface.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-04-01 at 13:05 +0100, Julien Grall wrote:
> On 04/01/2014 12:15 PM, Ian Campbell wrote:
> > On Tue, 2014-04-01 at 12:00 +0100, Julien Grall wrote:
> >> On 04/01/2014 11:49 AM, Ian Campbell wrote:
> >>> On Tue, 2014-04-01 at 11:46 +0100, Julien Grall wrote:
> >>>> On 04/01/2014 10:28 AM, Ian Campbell wrote:
> >>>>> On Tue, 2014-04-01 at 10:05 +0100, Julien Grall wrote:
> >>>>>> Out-of-context, I've noticed that most of trap failure will kill the 
> >>>>>> domain. From the ARM ARM , if a coprocessor instruction is failing, we 
> >>>>>> should         generate an Undefined Instruction exception (see P.7.5).
> >>>>>
> >>>>> You mean HSR_EC_CP15_32, HSR_EC_CP15_64 and HSR_EC_SYSREG?
> >>>>>
> >>>>> I've not checked but I think we only ask for traps for things which we
> >>>>> are supposed to be able to handle, so anything which is trapped which we
> >>>>> can't handle is a bug and would indicate the guest doing something
> >>>>> funky.
> >>>>
> >>>> Right, but if the emulation of the instruction fails (see
> >>>> vtimer_emulate, do_trap_psci,...), Xen will destroy the domain instead
> >>>> of sending an UNDEF exception.
> >>>
> >>> My point was that the emulation should never fail...
> >>
> >> The emulation can fail if the guest decides to write on an RO register.
> > 
> > Hrm yes, I'd forgotten that case.
> > 
> > Is that an undef or some other sort of exception? Perhaps it depends on
> > the cp register whether it faults or is ignored? In either case that
> > seems to suggest that it is up to the specific handler to inject the
> > correct kind of exception and return an appropriate error code to the
> > generic handler.
> 
> The default exception is "undefined instruction". I didn't find any
> specific exception following the coprocessor. Actually the only ways to
> kill the domain in traps.c:
>       - we try to access in read (resp. write) on WO (resp. RO) registers
>       - the hypercall tags is wrong
>       - the PSCI function is not implemented
> 
> I think we can replace every (?) domain_crash_synchronous by
> inject_undef*_exception.

Not in a bulk substitution. Each change would need justifying.

In the PSCI case I'd have thought the PSCI spec said what to do,
probably return some error code in r0? Or maybe not.

Ian.


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