RE: [v3 04/26] iommu, x86: Implement irq_set_vcpu_affinity for intel_ir_chip

[Wu, Feng]

> -----Original Message-----
> From: David Woodhouse [mailto:dwmw2@xxxxxxxxxxxxx]
> Sent: Wednesday, January 28, 2015 11:27 PM
> To: Wu, Feng
> Cc: tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx; x86@xxxxxxxxxx;
> gleb@xxxxxxxxxx; pbonzini@xxxxxxxxxx; joro@xxxxxxxxxx;
> alex.williamson@xxxxxxxxxx; jiang.liu@xxxxxxxxxxxxxxx; eric.auger@xxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx
> Subject: Re: [v3 04/26] iommu, x86: Implement irq_set_vcpu_affinity for
> intel_ir_chip
> 
> On Fri, 2014-12-12 at 23:14 +0800, Feng Wu wrote:
> > Implement irq_set_vcpu_affinity for intel_ir_chip.
> >
> > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > Reviewed-by: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
> 
> Acked-by: David.Woodhouse <David.Woodhouse@xxxxxxxxx> assuming a
> suitable answer to...
> 
> > +		vcpu_pi_info = (struct vcpu_data *)vcpu_info;
> > +		memcpy(irte_pi, &ir_data->irte_entry, sizeof(struct irte));
> > +
> > +		irte_pi->urg = 0;
> > +		irte_pi->vector = vcpu_pi_info->vector;
> > +		irte_pi->pda_l = (vcpu_pi_info->pi_desc_addr >>
> > +				 (32 - PDA_LOW_BIT)) & ~(-1UL << PDA_LOW_BIT);
> > +		irte_pi->pda_h = (vcpu_pi_info->pi_desc_addr >> 32) &
> > +				 ~(-1UL << PDA_HIGH_BIT);
> > +
> > +		irte_pi->__reserved_1 = 0;
> > +		irte_pi->__reserved_2 = 0;
> > +		irte_pi->__reserved_3 = 0;
> > +		irte_pi->__reserved_4 = 0;
> 
> .... do we need a barrier here before we set this bit?

Thanks a lot for your Ack, David!

I cannot find a reason why we need a barrier here, since 'irte_pi' is only a local
variant here, the real operation to program hardware occurs in modify_irte(), in
which spin lock is acquired, this means the there is an implicit barrier there.

Thanks,
Feng

> 
> > +		irte_pi->pst = 1;
> > +
> > +		modify_irte(&ir_data->irq_2_iommu, (struct irte *)irte_pi);
> 
> 
> --
> dwmw2
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