Re: [PATCH v12 for-xen-4.5 16/20] x86/VPMU: Handle PMU interrupts for PV guests

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

On 10/01/2014 10:26 AM, Jan Beulich wrote:
>
>>>>> Looking at the separation of hypervisor vs guest context to report
>>>>> again
>>>>>
>>>>>                /* Non-privileged domains are always in XENPMU_MODE_SELF mode */
>>>>>                if ( (vpmu_mode & XENPMU_MODE_SELF) ||
>>>>>                     (!is_hardware_domain(sampled->domain) &&
>>>>>                      !is_idle_vcpu(sampled)) )
>>>>>                    cur_regs = guest_cpu_user_regs();
>>>>>                else
>>>>>                    cur_regs = regs;
>>>>>
>>>>> I now additionally wonder why the condition here isn't just the SELF
>>>>> check: If the interrupt happened while in the hypervisor, why would
>>>>> you override this unconditionally to report a guest sample instead?
>>>>> Shouldn't the profiling domain tell you what it wants in that case
>>>>> (global vs guest local view)?
>>>> The second part of the check (!is_hardware_domain(sampled->domain) &&
>>>> !is_idle_vcpu(sampled)) is to prevent sending hypervisor sample to a
>>>> non-privileged guest. vpmu_mode may be, for example, XENPMU_MODE_HV but
>>>> that only means that dom0 can get hypervisor samples.
>>> Right, but that's not what the code above does: Instead of sending
>>> the hypervisor sample to Dom0 it converts it to a guest mode one.
>> Oh, I see --- when we get interrupted while in a non-privileged guest's
>> context (but in hypervisor) I send guest's registers, not Xen's.
>>
>> I think just SELF check is not sufficient though, we need to make sure
>> that we are not sending hypervisor sample to non-dom0. So
>>       if ( (vpmu_mode & XENPMU_MODE_SELF) ||
>> !is_hardware_domain(sampling->domain) )
> Actually I think instead the determination of sampling needs to
> depend on the register context rather than solely on the current
> domain's ID.

Not sure I follow this --- we do need to take domainID into account to 
avoid sending non-dom0 a hypervisor sample.

Or are you saying that what to send depends on both RIP and domainID?, 
Something like

     if ( (vpmu_mode & XENPMU_MODE_SELF) )
                 cur_regs = guest_cpu_user_regs();
     else if ( (regs->rip >= XEN_VIRT_START) && (regs->rip < 
XEN_VIRT_END) && is_hardware_domain(sampling->domain))
                 cur_regs = regs;
     else
                 cur_regs = guest_cpu_user_regs();

-boris