Re: [Xen-devel] [PATCH] xen/arm64: Avoid sending SGI when kicking secondary cpus with spin_table

[Julien Grall <julien.grall.oss@xxxxxxxxx>]

Hi Ian,

On 15/04/15 15:57, Ian Campbell wrote:
> On Wed, 2015-04-08 at 13:23 +0100, Julien Grall wrote:
>> Hi Chen,
>>
>> Subject: I think you can drop the "_" in spin_table.
>>
>> On 07/04/15 08:33, Chen Baozi wrote:
>>> From: Chen Baozi <baozich@xxxxxxxxx>
>>>
>>> On arm64, either firmware or xen's smp_up_cpu gate uses WFE on secondary
>>> cpus to stand-by when booting. Thus, using SEV is enough for the boot
>>> cpu to kick other secondaries. Further more, the current implementation
>>> of cpu_up_send_sgi would pass a NULL cpumask pointer to send_SGI, which
>>> then lead a data fault on GICv3 send_SGI implementation.
>>
>> I'm not familiar with spin table on ARM64, so I will let Ian answer
>> about it.
> 
> For arm32 it's sadly all a bit adhoc and not terribly well documented.
> (If I'm wrong I'd love a pointer to the doc). But for arm64 it does seem
> to be documented (linux/Documentation/arm64/booting.txt)

Thanks for the pointer.

[..]

> So, I dunno, it seems like there is a good chance we could remove this,
> but that might break some random platform which we have forgotten about.

Hmmm... I looked the wrong code in Linux :/.
The SGI is required for most of the platforms.

> The GIC NULL issue thing should probably fixed either way, but we could
> also try dropping the send SGI from both arm32 and 64 and see what
> happens...

I will see to rework send_SGI_self and send_SGI_allbutself.

Although I may not be able to send the patch before a couple of weeks.

Nonetheless, based on the doc this patch looks valid to me and can go
without the reworking because GICv3 is only supported on ARM64 which
won't require to send an SGI:

Reviewed-by: Julien Grall <julien.grall@xxxxxxxxxx>

Cheers,

-- 
Julien Grall

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