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

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Message-ID: <55956515.5050103@citrix.com>
Date:	Thu, 2 Jul 2015 17:21:41 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<david.vrabel@...rix.com>, <konrad.wilk@...cle.com>
CC:	<kevin.tian@...el.com>, <linux-kernel@...r.kernel.org>,
	<dietmar.hahn@...fujitsu.com>, <xen-devel@...ts.xen.org>,
	<jbeulich@...e.com>
Subject: Re: [Xen-devel] [PATCH v5 3/6] xen/PMU: Initialization code for Xen
 PMU

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@...rix.com>

David
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