[PATCH v4 07/10] ARM: Introduce MPIDR_LEVEL_SHIFT macro

[Vladimir Murzin]

On 13/09/16 11:12, Marc Zyngier wrote:
> On 13/09/16 10:04, Vladimir Murzin wrote:
>> On 13/09/16 09:38, Christoffer Dall wrote:
>>> On Mon, Sep 12, 2016 at 03:49:21PM +0100, Vladimir Murzin wrote:
>>>> vgic-v3 driver uses architecture specific MPIDR_LEVEL_SHIFT macro to
>>>> encode the affinity in a form compatible with ICC_SGI* registers.
>>>> Unfortunately, that macro is missing on ARM, so let's add it.
>>>>
>>>> Cc: Russell King <rmk+kernel at armlinux.org.uk>
>>>> Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
>>>> ---
>>>>  arch/arm/include/asm/cputype.h |    1 +
>>>>  1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h
>>>> index 1ee94c7..e2d94c1 100644
>>>> --- a/arch/arm/include/asm/cputype.h
>>>> +++ b/arch/arm/include/asm/cputype.h
>>>> @@ -55,6 +55,7 @@
>>>>  
>>>>  #define MPIDR_LEVEL_BITS 8
>>>>  #define MPIDR_LEVEL_MASK ((1 << MPIDR_LEVEL_BITS) - 1)
>>>> +#define MPIDR_LEVEL_SHIFT(level) (MPIDR_LEVEL_BITS * level)
>>>>  
>>>
>>> I'm not sure I follow the correctness of this completely.
>>>
>>> This is called from vgic_v3_dispatch_sgi, which takes a u64 value, which
>>> may have something in the Aff3 field, which we now shift left 24 bits,
>>> but that is not the Aff3 field of AArch32's MPIDR.
>>>
>>> What is the rationale for this making sense again?
>>
>> IIUC, in such case we construct mpidr which won't match in match_mpidr()
>> with the value we get from kvm_vcpu_get_mpidr_aff() and no SGI will be
>> sent to the guest.
>>
>> Since we get that u64 value from the guest, I'd think it is something
>> wrong is going on in the guest in case Aff3 is non-zero; however, we can
>> hide it by zeroing out SGI Aff3 bits in access_gic_sgi().
> 
> I don't think zeroing Aff3 is the right move, as the spec doesn't say
> that Aff3 should be ignored in a write to ICC_SGI1R. On the other hand,
> the spec says (in the context of the target list): "If a bit is 1 and
> the bit does not correspond to a valid target PE, the bit must be
> ignored by the Distributor".
> 
> This makes me think that, unless ICC_SGI1R.IMR is set, we should simply
> ignore that SGI because there is no way we can actually deliver it.
> 
> Could you cook a small patch that would go on top of this series?

I assume you've meant ICC_SGI1R.IRM, aka broadcast. In this case,
vgic_v3_dispatch_sgi() seems already matches the logic you've described:

- if IRM == 1, send to everyone except self without check for mpidr
- if IRM == 0, send to target iff matched to a valid mpidr

Am I missing something?

Thanks
Vladimir

> 
> Thanks,
> 
> 	M.
>