[Xen-devel] Re: XEN monitor/mwait patch for AMD SVM

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

No problem. In general, we aren't too afraid of having 'power user' options
in the domain config file that can cause real problems if misapplied.
Especially this CPUID config, which most end users have not a prayer of
understanding and probably should not touch at all unless told to. The
expectation is that most vendors will wrap up that layer with a GUI wizard
of some sort to hide most of the complexity and power.

 -- Keir

On 23/05/2009 15:26, "Boppuri, Navin" <Navin.Boppuri@xxxxxxx> wrote:

> :) Point taken! Thank you for considering the request though.
> 
> -Navin
> 
>> -----Original Message-----
>> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>> Sent: Friday, May 22, 2009 12:19 PM
>> To: Boppuri, Navin; xen-devel@xxxxxxxxxxxxxxxxxxx
>> Subject: Re: XEN monitor/mwait patch for AMD SVM
>> 
>> That's firmly in the 'Doctor, it hurts when I...' category I'm afraid. No
>> way will I apply this type of patch.
>> 
>>  -- Keir
>> 
>> On 22/05/2009 18:10, "Boppuri, Navin" <Navin.Boppuri@xxxxxxx> wrote:
>> 
>>> Keir,
>>> 
>>> Sorry but the patch is against the latest tip of the xen unstable tree
>>> (changeset: 18646).
>>> 
>>> I understand that MWAIT is not mentioned in the whitelist for HVM
>> policy.
>>> However, one could modify the guest config file and set the cpuid bit
>> for
>>> monitor/mwait and enable this feature by force. I was able to do just
>> this in
>>> my test configuration. This patch should cover such mods for cpuid in
>> addition
>>> to the cpuid policy in libxc.
>>> 
>>> Thank you.
>>> -Navin
>>> 
>>>> -----Original Message-----
>>>> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>>>> Sent: Friday, May 22, 2009 11:40 AM
>>>> To: Boppuri, Navin; xen-devel@xxxxxxxxxxxxxxxxxxx
>>>> Subject: Re: XEN monitor/mwait patch for AMD SVM
>>>> 
>>>> On 22/05/2009 16:23, "Boppuri, Navin" <Navin.Boppuri@xxxxxxx> wrote:
>>>> 
>>>>> This patch clears the monitor/mwait bit in the cpuid intercept code
>> for
>>>> AMD¹s
>>>>> SVM. This is to disallow VM¹s that may try and use the monitor/mwait
>>>> feature
>>>>> on AMD processors which is currently not supported in XEN.
>>>>> 
>>>>> Signed-off-by: Navin Boppuri <navin.boppuri@xxxxxxx>
>>>> 
>>>> What Xen version is this patch against? We already hide MWAIT from HVM
>>>> guests as far as I am aware. See
>>>> tools/libxc/xc_cpuid_x86.c:xc_cpuid_hvm_policy(), and note that
>> features
>>>> are
>>>> *whitelisted* and also that MWAIT is *not* mentioned.
>>>> 
>>>> So I think your patch is not needed, and also inappropriate since we
>>>> implement CPUID filtering policy in libxc these days.
>>>> 
>>>>  -- Keir
>>>> 
>>>> 
>>> 
>>> 
>> 
>> 
> 
> 



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