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

[marc.zyngier@arm.com (Marc Zyngier)]

On 14/09/16 16:21, Vladimir Murzin wrote:
> On 13/09/16 11:44, Marc Zyngier wrote:
>> On 13/09/16 11:32, Vladimir Murzin wrote:
>>> 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@armlinux.org.uk>
>>>>>>> Signed-off-by: Vladimir Murzin <vladimir.murzin@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,
>>
>> Yes, sorry.
>>
>>> 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?
>>
>> Not much. My only ask was that if Aff3 was set, we could take the
>> shortcut of not calling vgic_v3_dispatch_sgi() at all and return
>> immediately. But as you said, we already deal with the case of invalid
>> MPIDRs.
>>
> 
> Anything I can do to make this patch better?

I'm OK with it as it is. The shortcut doesn't bring anything useful, so
let's not optimise for an invalid case.

FWIW: Acked-by: Marc Zyngier <marc.zyngier@arm.com>

	M.
-- 
Jazz is not dead. It just smells funny...