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Re: [Xen-devel] [PATCH 1/3] [not-for-unstable] xen/arm: vgic-v3: Delay the initialization of the domain information
- To: Julien Grall <julien.grall@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 4 Sep 2018 20:53:10 +0100
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- Cc: andre.przywara@xxxxxxx, sstabellini@xxxxxxxxxx, shameerali.kolothum.thodi@xxxxxxxxxx
- Delivery-date: Tue, 04 Sep 2018 19:53:19 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 04/09/18 20:35, Julien Grall wrote:
> Hi,
>
> On 09/04/2018 08:21 PM, Julien Grall wrote:
>> A follow-up patch will require to know the number of vCPUs when
>> initializating the vGICv3 domain structure. However this information is
>> not available at domain creation. This is only known once
>> XEN_DOMCTL_max_vpus is called for that domain.
>>
>> In order to get the max vCPUs around, delay the domain part of the vGIC
>> v3 initialization until the first vCPU of the domain is initialized.
>>
>> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
>>
>> ---
>>
>> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>
>> This is nasty but I can't find a better way for Xen 4.11 and older. This
>> is not necessary for unstable as the number of vCPUs is known at domain
>> creation.
>>
>> Andrew, I have CCed you to know whether you have a better idea where to
>> place this call on Xen 4.11 and older.
>
> I just noticed that d->max_vcpus is initialized after
> arch_domain_create. So without this patch on Xen 4.12, it will not work.
>
> This is getting nastier because arch_domain_init is the one initialize
> the value returned by dom0_max_vcpus. So I am not entirely sure what
> to do here.
The positioning after arch_domain_create() is unfortunate, but I
couldn’t manage better with ARM's current behaviour and Jan's insistence
that the allocation of d->vcpu was common. I'd prefer if the dependency
could be broken and the allocation moved earlier.
One option might be to have an arch_check_domainconfig() (or similar?)
which is called very early on and can sanity check the values, including
cross-checking the vgic and max_vcpus settings? It could even be
responsible for mutating XEN_DOMCTL_CONFIG_GIC_NATIVE into the correct
real value.
As for your patch here, its a gross hack, but its probably the best
which can be done. I have to admit that I'm surprised/concerned that
Xen has lasted this long with such a fundamental gap in domain creation.
~Andrew
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