Re: [PATCH] use upstream cpuid code

[Glauber Costa <glommer@redhat.com>]

On Mon, Aug 03, 2009 at 05:06:28PM +0300, Avi Kivity wrote:
> On 08/03/2009 04:22 PM, Glauber Costa wrote:
>> On Mon, Aug 03, 2009 at 02:57:47PM +0300, Avi Kivity wrote:
>>    
>>> On 07/28/2009 11:05 PM, Glauber Costa wrote:
>>>      
>>>> use cpuid code from upstream. By doing that, we lose the following snippet
>>>> in kvm_get_supported_cpuid():
>>>>
>>>>       ret |= 1<<   12; /* MTRR */
>>>>       ret |= 1<<   16; /* PAT */
>>>>       ret |= 1<<   7;  /* MCE */
>>>>       ret |= 1<<   14; /* MCA */
>>>>
>>>> A quick search in mailing lists says this code is not really necessary, and we're
>>>> keeping it just for backwards compatibility. This is not that important, because
>>>> we'd lose it anyway in the golden day in which we totally merge with qemu.
>>>> Anyway, if it do _is_ important, we can send a patch to qemu with it.
>>>>
>>>>        
>>> It is important.  Please don't introduce regressions (if you do,
>>> introduce them in separate patches).  The procedure to drop such
>>> workarounds for kernel bugs is to verify that major distros have the
>>> kernel fixes in their supported kernels.
>>>      
>> Since this was introduced to fix a bug that did not even existed in Windows,
>> I can't see what you mean by "distro kernels" here.
>>    
>
> If qemu-kvm with this patch works on Fedora 10 (latest kernel) and the  
> equivalent opensuse and Ubuntu kernels, then we can safely remove the  
> bug workaround.  If not, if we apply the patch we just cause users  
> needless pain.
Again, since it was reported to fix a problem (that did not even existed in
the first place) with Windows Vista, I don't really know why shouldn'it
it work with any of the Linux guests (since they were not affected, to begin
with)

However, if you point me to a simple test case, I can definitely test it to make
sure no weird condition is taking place.