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

From: Julien Grall <julien.grall@citrix.com>
To: Chen Baozi <cbz@baozis.org>, xen-devel@lists.xen.org
Cc: Chen Baozi <baozich@gmail.com>,
	julien.grall@linaro.org, ian.campbell@citrix.com
Subject: Re: [PATCH] xen/arm64: Avoid sending SGI when kicking secondary cpus with spin_table
Date: Wed, 8 Apr 2015 13:23:13 +0100	[thread overview]
Message-ID: <55251DB1.6050504@citrix.com> (raw)
In-Reply-To: <1428392032-11551-1-git-send-email-cbz@baozis.org>

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@gmail.com>
> 
> 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.

Aside that, the GICv3 implementation looks buggy to me.
The GIC code provides two helpers which lead to pass NULL to the
callback send_SGI:
	- send_SGI_self: AFAICT nobody is using it
	- send_SGI_allbutself: Only used by the smp boot code

I think the former can be dropped or modify to send_SGI_one.

For the later, I can't find why we need to send an SGI on ARM too. Ian,
Stefano, any idea?

Regards.

-- 
Julien Grall