From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@suse.com>
Subject: Re: [PATCH v18 07/16] x86/VPMU: Initialize PMU for
 PV(H) guests
Date: Fri, 20 Feb 2015 14:35:04 +0000
Message-ID: <54E754280200007800062148@mail.emea.novell.com>
References: <1424125619-10851-1-git-send-email-boris.ostrovsky@oracle.com>
	<1424125619-10851-8-git-send-email-boris.ostrovsky@oracle.com>
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To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: kevin.tian@intel.com, suravee.suthikulpanit@amd.com, andrew.cooper3@citrix.com, tim@xen.org, dietmar.hahn@ts.fujitsu.com, xen-devel@lists.xen.org, Aravind.Gopalakrishnan@amd.com, jun.nakajima@intel.com, dgdegra@tycho.nsa.gov
List-Id: xen-devel@lists.xenproject.org

>>> On 16.02.15 at 23:26, <boris.ostrovsky@oracle.com> wrote:
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -437,6 +437,8 @@ int vcpu_initialise(struct vcpu *v)
>          vmce_init_vcpu(v);
>      }
>  
> +    spin_lock_init(&v->arch.vpmu.vpmu_lock);

This would rather seem to belong into vpmu_initialize().

> @@ -503,6 +509,16 @@ int __init amd_vpmu_init(void)
>          return -EINVAL;
>      }
>  
> +    if ( sizeof(struct xen_pmu_data) +
> +         2 * sizeof(uint64_t) * num_counters > PAGE_SIZE )
> +    {
> +        printk(XENLOG_WARNING
> +               "VPMU: Register bank does not fit into VPMU shared page\n");
> +        counters = ctrls = NULL;
> +        num_counters = 0;
> +        return -ENOSPC;
> +    }

Wouldn't it be more reasonable to simply lower num_counters in
that case?

> +static int pvpmu_init(struct domain *d, xen_pmu_params_t *params)
> +{
> +    struct vcpu *v;
> +    struct vpmu_struct *vpmu;
> +    struct page_info *page;
> +    uint64_t gfn = params->val;
> +
> +    if ( vpmu_mode == XENPMU_MODE_OFF )
> +        return -EINVAL;
> +
> +    if ( (params->vcpu >= d->max_vcpus) || (d->vcpu == NULL) ||
> +         (d->vcpu[params->vcpu] == NULL) )
> +        return -EINVAL;
> +
> +    if ( v->arch.vpmu.xenpmu_data )
> +        return -EINVAL;
> +
> +    page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
> +    if ( !page )
> +        return -EINVAL;
> +
> +    if ( !get_page_type(page, PGT_writable_page) )
> +    {
> +        put_page(page);
> +        return -EINVAL;
> +    }
> +
> +    v = d->vcpu[params->vcpu];
> +    vpmu = vcpu_vpmu(v);
> +    spin_lock(&vpmu->vpmu_lock);
> +
> +    v->arch.vpmu.xenpmu_data = __map_domain_page_global(page);
> +    if ( !v->arch.vpmu.xenpmu_data )
> +    {
> +        put_page_and_type(page);
> +        spin_unlock(&vpmu->vpmu_lock);
> +        return -EINVAL;
> +    }
> +
> +    vpmu_initialise(v);
> +
> +    spin_unlock(&vpmu->vpmu_lock);

So what is this lock guarding against here? Certainly not overwriting
of a non-NULL v->arch.vpmu.xenpmu_data (and hence leaking a
page reference)...

> @@ -504,7 +590,7 @@ long do_xenpmu_op(unsigned int op, XEN_GUEST_HANDLE_PARAM(xen_pmu_params_t) arg)
>  
>          if ( copy_to_guest(arg, &pmu_params, 1) )
>              return -EFAULT;
> -        break;
> +         break;

???

Jan