Re: [Xen-devel] [PATCH v9 1/3] xen/libxc: Allow changing max number of hypervisor cpuid leaves

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Jan Beulich wrote on 2014-04-23:
>>>> On 23.04.14 at 10:42, <Ian.Campbell@xxxxxxxxxx> wrote:
>> On Tue, 2014-04-22 at 15:17 -0400, Boris Ostrovsky wrote:
>>> Add support for changing max number of hypervisor leaves from
>>> configuration file.
>>> 
>>> This number can be specified using xl's standard 'cpuid' option. Only
>>> lowest 8 bits of leaf's 0x4000xx00 eax register are processed, all
>>> others are ignored.
>>> 
>>> The changes allow us to revert commit
>>> 80ecb40362365ba77e68fc609de8bd3b7208ae19 which is most likely no
>>> longer needed now anyway (Solaris bug that it addressed has been fixed
>>> and backported to earlier releases) but leave possibility of running
>>> unpatched version of Solaris by forcing number of leaves to 2 in the
>>> configuration file.
>>> 
>>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>> 
>> I'm happy with this if Jan is:
>>         Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> 
> I am (minus the stray printk() in patch 3 that I just commented on).
> 
>> I assume Jan will apply along with the h/v side.
> 
> I'll definitely want a VMX maintainer's ack (or at least Yang's
> consent) on patch
> 3 before applying the whole series (the first two patches alone don't
> make that much sense).

I have discussed with Boris before (offlist) and I don't think it is necessary 
to expose two bits. Per my understanding, only one bit to indicate whether 
APICv is enabled should be enough. The reason is that all hardwires that 
support APICv must also support virtualized x2apic(Intel SDM doesn't say it 
explicitly, but I get confirmed from hardware guys). And in current Xen's 
implementation, it will enable APICv and virtualize_x2apic unconditionally if 
hardware support them and not disabled by user. So based on current xen's 
implementation, APICv is enabled means virtulized x2apic is enabled, vice 
versa. That's the reason why I think one bit is enough.
But if you guys think two bits also is acceptable, I am ok.

> 
> Jan


Best regards,
Yang


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