Re: [PATCH v25 04/15] x86/VPMU: Interface for setting PMU mode and flags

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

On 06/22/2015 11:10 AM, Jan Beulich wrote:
>
>> +    switch ( op )
>> +    {
>> +    case XENPMU_mode_set:
>> +    {
>> +        if ( (pmu_params.val & ~(XENPMU_MODE_SELF | XENPMU_MODE_HV)) ||
>> +             (hweight64(pmu_params.val) > 1) )
>> +            return -EINVAL;
>> +
>> +        /* 32-bit dom0 can only sample itself. */
>> +        if ( is_pv_32bit_vcpu(current) && (pmu_params.val & XENPMU_MODE_HV) )
>> +            return -EINVAL;
>> +
>> +        spin_lock(&vpmu_lock);
>> +
>> +        /*
>> +         * We can always safely switch between XENPMU_MODE_SELF and
>> +         * XENPMU_MODE_HV while other VPMUs are active.
>> +         */
>> +        if ( (vpmu_count == 0) || (vpmu_mode == pmu_params.val) ||
>> +             ((vpmu_mode ^ pmu_params.val) ==
>> +              (XENPMU_MODE_SELF | XENPMU_MODE_HV)) )
>> +            vpmu_mode = pmu_params.val;
>> +        else
>> +        {
> I think this would better be
>
>          if ( (vpmu_count == 0) ||
>               ((vpmu_mode ^ pmu_params.val) ==
>                (XENPMU_MODE_SELF | XENPMU_MODE_HV)) )
>              vpmu_mode = pmu_params.val;
>          else if ( vpmu_mode != pmu_params.val )
>          {
>
> But there's no need to re-submit just because of this (it could be
> changed upon commit if you agree).

This will generate an error (with a message to the log) even if we keep 
the mode unchanged, something that I wanted to avoid. (Same thing for 
XENPMU_feature_set, which is what Kevin mentioned last time).

>
> Or wait - I just checked again, and while I thought this was long
> addressed I still don't seen struct xen_pmu_params "pad" field
> being checked to be zero as input, and being stored as zero when
> only an output. Did this get lost? Did I forget about a reason why
> this isn't being done? Unless the latter is the case, the ack above
> is dependent upon this getting fixed.


Yes, we did talk about this and as result I added major version check 
(which I should have had there anyway): if we decide to start using this 
field we'd need to increment the major version.

-boris