Re: [Xen-devel] [PATCH v12 03/18] xen/pvh: Early bootup changes in PV code (v2).

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 03/01/14 01:34, Mukesh Rathor wrote:
> On Thu, 2 Jan 2014 13:32:21 -0500
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> 
>> On Thu, Jan 02, 2014 at 03:32:33PM +0000, David Vrabel wrote:
>>> On 01/01/14 04:35, Konrad Rzeszutek Wilk wrote:
>>>> From: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
>>>>
>>>> In the bootup code for PVH we can trap cpuid via vmexit, so don't
>>>> need to use emulated prefix call. We also check for vector
>>>> callback early on, as it is a required feature. PVH also runs at
>>>> default kernel IOPL.
>>>>
>>>> Finally, pure PV settings are moved to a separate function that
>>>> are only called for pure PV, ie, pv with pvmmu. They are also
>>>> #ifdef with CONFIG_XEN_PVMMU.
>>> [...]
>>>> @@ -331,12 +333,15 @@ static void xen_cpuid(unsigned int *ax,
>>>> unsigned int *bx, break;
>>>>    }
>>>>  
>>>> -  asm(XEN_EMULATE_PREFIX "cpuid"
>>>> -          : "=a" (*ax),
>>>> -            "=b" (*bx),
>>>> -            "=c" (*cx),
>>>> -            "=d" (*dx)
>>>> -          : "0" (*ax), "2" (*cx));
>>>> +  if (xen_pvh_domain())
>>>> +          native_cpuid(ax, bx, cx, dx);
>>>> +  else
>>>> +          asm(XEN_EMULATE_PREFIX "cpuid"
>>>> +                  : "=a" (*ax),
>>>> +                  "=b" (*bx),
>>>> +                  "=c" (*cx),
>>>> +                  "=d" (*dx)
>>>> +                  : "0" (*ax), "2" (*cx));
>>>
>>> For this one off cpuid call it seems preferrable to me to use the
>>> emulate prefix rather than diverge from PV.
>>
>> This was before the PV cpuid was deemed OK to be used on PVH.
>> Will rip this out to use the same version.
> 
> Whats wrong with using native cpuid? That is one of the benefits that
> cpuid can be trapped via vmexit, and also there is talk of making PV
> cpuid trap obsolete in the future. I suggest leaving it native.

It should either use the PV interface or the HVM one, not a hybrid of
the two.

David

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel