Re: [PATCH v6 11/19] x86/VPMU: Initialize PMU for PV guests

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 05/21/2014 04:01 AM, Jan Beulich wrote:
>>>> On 20.05.14 at 19:47, <boris.ostrovsky@oracle.com> wrote:
>> On 05/20/2014 11:51 AM, Jan Beulich wrote:
>>>>>> On 13.05.14 at 17:53, <boris.ostrovsky@oracle.com> wrote:
>>>> --- a/xen/arch/x86/hvm/svm/svm.c
>>>> +++ b/xen/arch/x86/hvm/svm/svm.c
>>>> @@ -1150,7 +1150,8 @@ static int svm_vcpu_initialise(struct vcpu *v)
>>>>            return rc;
>>>>        }
>>>>    
>>>> -    vpmu_initialise(v);
>>>> +    if ( is_hvm_domain(v->domain) )
>>>> +        vpmu_initialise(v);
>>> Why?
>> This patch adds initialization for PV domains, which is conditioned by
>> is_pv_domain() in amd_vpmu_initialise()/core2_vpmu_alloc_resource(). I
>> don't want PVH domains (which call these routines) to try to set up
>> their VPMUs from here. This is supposed to happen via pvpmu_init()
>> (which in this patch will return -EINVAL for PVH).
> So what's the reason for making PVH PV-like here rather than
> HVM-like? With the intended goal of making PVH a HVM sub-mode,
> that'll require more exceptions in the long run.


Primarily because of interrupt handling: we don't end up in HVM guest's 
interrupt handler for PMU interrupts but rather in the PV PMU_VIRQ 
handler which expects shared context to be set up. This means that 
initialization for PVH has to be slightly different.

-boris