Re: [Xen-devel] [PATCH v5 3/6] xen/PMU: Initialization code for Xen PMU

[David Vrabel <david.vrabel@citrix.com>]

On 02/07/15 15:53, Boris Ostrovsky wrote:
> Map shared data structure that will hold CPU registers, VPMU context,
> V/PCPU IDs of the CPU interrupted by PMU interrupt. Hypervisor fills
> this information in its handler and passes it to the guest for further
> processing.
> 
> Set up PMU VIRQ.
> 
> Now that perf infrastructure will assume that PMU is available on a PV
> guest we need to be careful and make sure that accesses via RDPMC
> instruction don't cause fatal traps by the hypervisor. Provide a nop
> RDPMC handler.
> 
> For the same reason avoid issuing a warning on a write to APIC's LVTPC.
> 
> Both of these will be made functional in later patches.
[...]
> +		rc = bind_virq_to_irqhandler(VIRQ_XENPMU, cpu,
> +					     xen_pmu_irq_handler,
> +					     IRQF_PERCPU|IRQF_NOBALANCING,
> +					     pmu_name, NULL);

If you bind a VIRQ as IRQF_PERCPU it can only be safely unbound on the
CPU it is bound to (because the percpu handler does not take the
desc->lock).

Otherwise, Reviewed-by: David Vrabel <david.vrabel@citrix.com>

David