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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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


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