Re: [PATCH v4 14/16] xen/arm: Add virtual GICv3 support

[Julien Grall <julien.grall@linaro.org>]

On 06/02/2014 05:38 PM, Ian Campbell wrote:
> On Mon, 2014-06-02 at 17:18 +0100, Julien Grall wrote:
>> On 06/02/2014 05:15 PM, Ian Campbell wrote:
>>> On Mon, 2014-06-02 at 17:10 +0100, Julien Grall wrote:
>>>>
>>>>> diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
>>>>> index 3fa0857..787c547 100644
>>>>> --- a/xen/arch/arm/vgic.c
>>>>> +++ b/xen/arch/arm/vgic.c
>>>>> @@ -264,10 +264,19 @@ int domain_vgic_init(struct domain *d)
>>>>>      else
>>>>>          d->arch.vgic.nr_lines = 0; /* We don't need SPIs for the guest */
>>>>>  
>>>>> -    if ( gic_hw_version() == GIC_V2 )
>>>>> +    switch ( gic_hw_version() )
>>>>> +    {
>>>>> +#ifdef CONFIG_ARM_64
>>>>> +    case GIC_V3:
>>>>> +        vgic_v3_init(d);
>>>>> +        break;
>>>>> +#endif
>>>>> +    case GIC_V2:
>>>>>          vgic_v2_init(d);
>>>>> -    else
>>>>> +        break;
>>>>> +    default:
>>>>>          panic("No VGIC found\n");
>>>>
>>>> I think I've already said in an earlier patch. Please avoid to use panic
>>>> when this function is called by a VM.
>>>
>>> Whether called from a guest or not, gic_hw_version's result is, I think,
>>> completely under hypervisor control, if it returns a gic version which
>>> we don't support then that is worthy of a panic() I think, or a
>>> BUG_ON(), since that is a hypervisor coding issue.
>>
>> It won't be under hypervisor control if we add an hypercall to choose
>> whether we want to use GICv2 or GICv3.
> 
> That (tools only) hypercall should obviously validate that it knows
> about the gic that is being asked for at the time.
> 
> If on retrieval it is not something we understand then that is still a
> hypervisor bug.

Assuming we correctly validated the version given by the toolstack. I'm
not very confident with a BUG_ON/panic in hypercall (this function is
called during domain creation) when we can just return an error code and
safely come back in a valid state (i.e nothing will leak...)

Regards,

-- 
Julien Grall