Re: [PATCH 2/4] KVM: arm/arm64: re-create event when setting counter value

[Andrew Murray <andrew.murray@arm.com>]

On Tue, Jan 22, 2019 at 12:12:51PM +0000, Julien Thierry wrote:
> Hi Andrew,
> 
> On 22/01/2019 10:49, Andrew Murray wrote:
> > The perf event sample_period is currently set based upon the current
> > counter value, when PMXEVTYPER is written to and the perf event is created.
> > However the user may choose to write the type before the counter value in
> > which case sample_period will be set incorrectly. Let's instead decouple
> > event creation from PMXEVTYPER and (re)create the event in either
> > suitation.
> > 
> > Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> > ---
> >  virt/kvm/arm/pmu.c | 39 ++++++++++++++++++++++++++++++---------
> >  1 file changed, 30 insertions(+), 9 deletions(-)
> > 
> > diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> > index 531d27f..4464899 100644
> > --- a/virt/kvm/arm/pmu.c
> > +++ b/virt/kvm/arm/pmu.c
> > @@ -24,6 +24,8 @@
> >  #include <kvm/arm_pmu.h>
> >  #include <kvm/arm_vgic.h>
> >  
> > +static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 data,
> > +				      u64 select_idx);
> >  /**
> >   * kvm_pmu_get_counter_value - get PMU counter value
> >   * @vcpu: The vcpu pointer
> > @@ -57,11 +59,18 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
> >   */
> >  void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val)
> >  {
> > -	u64 reg;
> > +	u64 reg, data;
> >  
> >  	reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
> >  	      ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + select_idx;
> >  	__vcpu_sys_reg(vcpu, reg) += (s64)val - kvm_pmu_get_counter_value(vcpu, select_idx);
> > +
> > +	reg = (select_idx == ARMV8_PMU_CYCLE_IDX)
> > +	      ? PMCCFILTR_EL0 : PMEVTYPER0_EL0 + select_idx;
> > +	data = __vcpu_sys_reg(vcpu, reg + select_idx);
> 
> I think this should be just "reg" instead of "reg + select_idx".

Yes, good catch.

Thanks,

Andrew Murray

> 
> Cheers,
> 
> -- 
> Julien Thierry

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