linux-kernel - RE: [v3 04/26] iommu, x86: Implement irq_set_vcpu_affinity for intel_ir

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Date:	Thu, 29 Jan 2015 07:55:24 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	David Woodhouse <dwmw2@...radead.org>
CC:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"gleb@...nel.org" <gleb@...nel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"joro@...tes.org" <joro@...tes.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [v3 04/26] iommu, x86: Implement irq_set_vcpu_affinity for
 intel_ir_chip



> -----Original Message-----
> From: David Woodhouse [mailto:dwmw2@...radead.org]
> Sent: Wednesday, January 28, 2015 11:27 PM
> To: Wu, Feng
> Cc: tglx@...utronix.de; mingo@...hat.com; hpa@...or.com; x86@...nel.org;
> gleb@...nel.org; pbonzini@...hat.com; joro@...tes.org;
> alex.williamson@...hat.com; jiang.liu@...ux.intel.com; eric.auger@...aro.org;
> linux-kernel@...r.kernel.org; iommu@...ts.linux-foundation.org;
> kvm@...r.kernel.org
> 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@...el.com>
> > Reviewed-by: Jiang Liu <jiang.liu@...ux.intel.com>
> 
> Acked-by: David.Woodhouse <David.Woodhouse@...el.com> 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