Re: [PATCH v20 02/13] x86/VPMU: Add public xenpmu.h

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 04/20/2015 04:50 AM, Jan Beulich wrote:
>>>> On 09.04.15 at 17:44, <boris.ostrovsky@oracle.com> wrote:
>> --- /dev/null
>> +++ b/xen/include/public/pmu.h
>> @@ -0,0 +1,38 @@
>> +#ifndef __XEN_PUBLIC_PMU_H__
>> +#define __XEN_PUBLIC_PMU_H__
>> +
>> +#include "xen.h"
>> +#if defined(__i386__) || defined(__x86_64__)
>> +#include "arch-x86/pmu.h"
>> +#elif defined (__arm__) || defined (__aarch64__)
>> +#include "arch-arm.h"
>> +#else
>> +#error "Unsupported architecture"
>> +#endif
>> +
>> +#define XENPMU_VER_MAJ    0
>> +#define XENPMU_VER_MIN    1
>> +
>> +
>> +/* Shared between hypervisor and PV domain */
>> +struct xen_pmu_data {
> Iirc this sharing is r/o - if so, please state so in the comment. If not,
> please extend the comment to briefly explain why writable sharing
> is safe/secure.

This data structure is writeable by guest (specifically, PMU registers 
and APIC_LVTPC). There is a flag (PMU_CACHED, which is part of this 
structure) that the hypervisor sets to let the guest know that it can 
write those fields without having to trap. When the guest is done, it 
issues XENPMU_flush command and the hypervisor writes out those values 
to HW.

I'll update the comments to make this clear.

-boris