Re: [PATCH v8 07/27] ARM: vGICv3: handle virtual LPI pending and property tables

[Julien Grall <julien.grall@arm.com>]

On 12/04/17 14:12, Andre Przywara wrote:
> Hi,

Hi,

>
> On 12/04/17 11:55, Julien Grall wrote:
>> Hi Andre,
>>
>> On 12/04/17 01:44, Andre Przywara wrote:
>>> Allow a guest to provide the address and size for the memory regions
>>> it has reserved for the GICv3 pending and property tables.
>>> We sanitise the various fields of the respective redistributor
>>> registers.
>>> The MMIO read and write accesses are protected by locks, to avoid any
>>> changing of the property or pending table address while a redistributor
>>> is live and also to protect the non-atomic vgic_reg64_extract() function
>>> on the MMIO read side.
>>>
>>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>>> Reviewed-by: Julien Grall <julien.grall@arm.com>
>>
>> Whilst I gave my reviewed-by it is very rude to ignore a comment.
>
> Yeah, sorry about that! I was unsure about that as well, so thought
> about it and eventually forgot to answer.
>
>> It would have been nicer to answer even if it is just saying "I can add
>> a TODO and address it in a follow-up patch".
>>
>> Please get use to mention all the changes (e.g the spin_*lock ->
>> spin_*lock_irq* change) you made in a patch. Mainly if you keep a
>> reviewed-by.
>
> I was really unsure about keeping or dropping it, but since you
> complained about me dropping it last time I tried it the other way this
> time ;-)
>
>>> diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
>>> index ebaea35..b2d98bb 100644
>>> --- a/xen/include/asm-arm/domain.h
>>> +++ b/xen/include/asm-arm/domain.h
>>> @@ -109,11 +109,15 @@ struct arch_domain
>>>          } *rdist_regions;
>>>          int nr_regions;                     /* Number of rdist
>>> regions */
>>>          uint32_t rdist_stride;              /* Re-Distributor stride */
>>> +        unsigned long int nr_lpis;
>>> +        uint64_t rdist_propbase;
>>>          struct rb_root its_devices;         /* Devices mapped to an
>>> ITS */
>>>          spinlock_t its_devices_lock;        /* Protects the
>>> its_devices tree */
>>>          struct radix_tree_root pend_lpi_tree; /* Stores struct
>>> pending_irq's */
>>>          rwlock_t pend_lpi_tree_lock;        /* Protects the
>>> pend_lpi_tree */
>>>          unsigned int intid_bits;
>>> +        bool rdists_enabled;                /* Is any redistributor
>>> enabled? */
>>> +        bool has_its;
>>
>> The comment you ignore was the one about consolidating rdists_enabled
>> and has_its in a single field and use flags.
>
> Yes, I had the idea myself before, but decided against it as IMHO it
> looks much nicer this way (compared to using a flags variable. which I
> guess is what you mean).
>
> Are you OK with that?

Why is it nicer? You only need 1 bit to represent rdist_enabled and 
another for has_its. This would save a bit a space in a resource limited 
structure. I would be OK with a TODO so we know we can save space here 
in the future...

Although, my main point was you not ignore comment and say no if you 
disagree.

Cheers,

-- 
Julien Grall

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