Re: [Xen-devel] [PATCH v3 3/6] xen/PMU: Initialization code for Xen PMU

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 07/04/2014 06:52 AM, David Vrabel wrote:
> On 03/07/14 20:14, 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 availble 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.
> [...]
> > +int xen_pmu_init(int cpu)
> > +{
> > +       int ret = 0;
> > +       struct xen_pmu_params xp;
> > +       unsigned long pfn;
> > +       struct xen_pmu_data *xenpmu_data;
> > +
> > +       BUILD_BUG_ON(sizeof(struct xen_pmu_data) > PAGE_SIZE);
> > +       xenpmu_data = vzalloc(PAGE_SIZE);
> Why vzalloc() for something that is only a page in size?
I need it page-aligned and I don't think kmalloc() guarantees that (the 
implementation might, but not the interface itself). I can use 
__get_free_page(), I suppose.
-boris

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