Re: [Xen-devel] [PATCH v4 10/17] x86/VPMU: Initialize PMU for PV guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.01.14 at 20:08, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> +static int pvpmu_init(struct domain *d, xen_pmu_params_t *params)
> +{
> +    struct vcpu *v;
> +    struct page_info *page;
> +    uint64_t gmfn = params->d.val;
> +
> +    if ( params->vcpu < 0 || params->vcpu >= d->max_vcpus )
> +        return -EINVAL;
> +
> +    page = get_page_from_gfn(d, gmfn, NULL, P2M_ALLOC);
> +    if ( !page )
> +        return -EINVAL;
> +
> +    v = d->vcpu[params->vcpu];
> +    v->arch.vpmu.xenpmu_data = __map_domain_page_global(page);
> +    if ( !v->arch.vpmu.xenpmu_data )
> +    {
> +        put_page(page);
> +        return -EINVAL;
> +    }
> +
> +    vpmu_initialise(v);
> +
> +    return 0;
> +}

This being for a PV guest, you need to obtain a write type reference
to the page, or else you risk the guest re-using the page for
something that mustn't be written to in uncontrolled ways (like a
page or descriptor table). See e.g. map_vcpu_info().

Jan


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