Re: [Qemu-arm] [PATCH v9 04/14] hw/arm/smmuv3: Skeleton

[Auger Eric <eric.auger@redhat.com>]

Hi Peter,

On 09/03/18 14:37, Peter Maydell wrote:
> On 9 March 2018 at 13:19, Auger Eric <eric.auger@redhat.com> wrote:
>> On 08/03/18 15:27, Peter Maydell wrote:
>>> Consider specifically catching 8-byte accesses to non-64-bit registers?
>>> This is CONSTRAINED UNPREDICTABLE (see spec section 6.2), and "one
>>> of the registers is read/written and other half is RAZ/WI" is permitted
>>> behaviour, but it does mean you need to be a little careful about not
>>> letting the top 32 bits of val become non-zero for the 32-bit register
>>> codepaths. Logging bad 64-bit accesses as LOG_GUEST_ERROR and making
>>> them RAZ/WI might be nicer for guest software developers.
>>
>> I moved to ops with attrs and if a 64-bit access is attempted on
>> something not a 64b reg base, I return an error + log a guest error.
> 
> Ah, you probably don't want to return MEMTX_ERROR, because that
> becomes a guest CPU external-abort exception. An abort is listed
> as one of the permitted constrained-unpredictable behaviours for
> bad 64-bit accesses, but there is a note that "strongly recommends"
> not to abort for cases where the registers might be used by software
> associated with lower exception levels. Rather than trying to decide
> which registers do or don't get to return MEMTX_ERROR, it's probably
> easier just to RAZ/WI and return MEMTX_OK.
> 
> (We had to fix a bug like this in the gicv3 in commits f1945632b43e3
> and 0cf09852015e when we started making MEMTX_ERROR generate aborts,
> though in that case the spec is more definite that abort is not a
> permitted behaviour.)

Yes saw those modifs in gic. I will check & fix this.

Thanks

Eric
> 
> thanks
> -- PMM
>