Re: [PATCH v9 09/20] x86/VPMU: Add public xenpmu.h

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

On 08/11/2014 10:08 AM, Jan Beulich wrote:
>>>> On 08.08.14 at 18:55, <boris.ostrovsky@oracle.com> wrote:
>>   static int amd_vpmu_initialise(struct vcpu *v)
>>   {
>> -    struct amd_vpmu_context *ctxt;
>> +    struct xen_pmu_amd_ctxt *ctxt;
>>       struct vpmu_struct *vpmu = vcpu_vpmu(v);
>>       uint8_t family = current_cpu_data.x86;
>>   
>> @@ -382,7 +386,8 @@ static int amd_vpmu_initialise(struct vcpu *v)
>>   	 }
>>       }
>>   
>> -    ctxt = xzalloc(struct amd_vpmu_context);
>> +    ctxt = xzalloc_bytes(sizeof(struct xen_pmu_amd_ctxt) +
>> +                         2 * sizeof(uint64_t) * AMD_MAX_COUNTERS);
> So I guess this is one of said sizeof()-s, and I continue to think this
> would benefit from using a proper field. It is my understanding that
> the real (non-C89 compliant) declaration of struct xen_pmu_amd_ctxt
> would be
>
> struct xen_pmu_amd_ctxt {
>      /* Offsets to counter and control MSRs (relative to xen_arch_pmu.c.amd) */
>      uint32_t counters;
>      uint32_t ctrls;
>      uint64_t values[];
> };

OK, this should work.

>
> Just like already done elsewhere you _can_ add variable-sized
> arrays to the public interface as long as you guard them suitably.
> And then your statement would become
>
>      ctxt = xzalloc_bytes(sizeof(*ctxt) +
>                           2 * sizeof(*ctxt->values) * AMD_MAX_COUNTERS);
>
> making clear what the allocation is doing.
>
>> @@ -391,7 +396,11 @@ static int amd_vpmu_initialise(struct vcpu *v)
>>           return -ENOMEM;
>>       }
>>   
>> +    ctxt->counters = sizeof(struct xen_pmu_amd_ctxt);
>> +    ctxt->ctrls = ctxt->counters + sizeof(uint64_t) * AMD_MAX_COUNTERS;
>      ctxt->counters = sizeof(*ctxt);
>      ctxt->ctrls = ctxt->counters + sizeof(*ctxt->values) * AMD_MAX_COUNTERS;
>
> or
>
>      ctxt->counters = offsetof(typeof(ctxt), values[0]);
>      ctxt->ctrls = offsetof(typeof(ctxt), values[AMD_MAX_COUNTERS]);
>
>> @@ -228,6 +229,9 @@ void vpmu_initialise(struct vcpu *v)
>>       struct vpmu_struct *vpmu = vcpu_vpmu(v);
>>       uint8_t vendor = current_cpu_data.x86_vendor;
>>   
>> +    BUILD_BUG_ON(sizeof(struct xen_pmu_intel_ctxt) > XENPMU_CTXT_PAD_SZ);
>> +    BUILD_BUG_ON(sizeof(struct xen_pmu_amd_ctxt) > XENPMU_CTXT_PAD_SZ);
> Don't these need to include the variable size array portions too?

Not in BUILD_BUG_ON but I should check whether I have enough space when 
computing ctxt->{ctrls | counters}.

-boris