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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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

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