RE: [v3 06/26] iommu, x86: No need to migrating irq for VT-d Posted-Interrupts

[Wu, Feng]

> -----Original Message-----
> From: Zhang, Yang Z
> Sent: Thursday, December 18, 2014 10:26 PM
> To: Wu, Feng; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx;
> x86@xxxxxxxxxx; gleb@xxxxxxxxxx; pbonzini@xxxxxxxxxx;
> dwmw2@xxxxxxxxxxxxx; joro@xxxxxxxxxx; alex.williamson@xxxxxxxxxx;
> jiang.liu@xxxxxxxxxxxxxxx
> Cc: eric.auger@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; Wu, Feng
> Subject: RE: [v3 06/26] iommu, x86: No need to migrating irq for VT-d
> Posted-Interrupts
> 
> Feng Wu wrote on 2014-12-12:
> > We don't need to migrate the irqs for VT-d Posted-Interrupts here.
> > When 'pst' is set in IRTE, the associated irq will be posted to guests
> > instead of interrupt remapping. The destination of the interrupt is
> > set in Posted-Interrupts Descriptor, and the migration happens during
> > vCPU scheduling.
> >
> > However, we still update the cached irte here, which can be used when
> > changing back to remapping mode.
> >
> > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > Reviewed-by: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/iommu/intel_irq_remapping.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > diff --git a/drivers/iommu/intel_irq_remapping.c
> > b/drivers/iommu/intel_irq_remapping.c index 48c2051..ab9057a 100644 ---
> > a/drivers/iommu/intel_irq_remapping.c +++
> > b/drivers/iommu/intel_irq_remapping.c @@ -977,6 +977,7 @@
> > intel_ir_set_affinity(struct irq_data *data, const struct cpumask *mask,
> >  {
> >  	struct intel_ir_data *ir_data = data->chip_data; 	struct irte *irte =
> >  &ir_data->irte_entry; +	struct irte_pi *irte_pi = (struct irte_pi
> >  *)irte; 	struct irq_cfg *cfg = irqd_cfg(data); 	struct irq_data *parent
> >  = data->parent_data; 	int ret;
> > @@ -991,7 +992,10 @@ intel_ir_set_affinity(struct irq_data *data,
> > const struct cpumask *mask,
> >  	 */
> >  	irte->vector = cfg->vector;
> >  	irte->dest_id = IRTE_DEST(cfg->dest_apicid);
> > -	modify_irte(&ir_data->irq_2_iommu, irte);
> > +
> > +	/* We don't need to modify irte if the interrupt is for posting. */
> > +	if (irte_pi->pst != 1)
> > +		modify_irte(&ir_data->irq_2_iommu, irte);
> 
> What happens if user changes the IRQ affinity manually?

If the IRQ is posted, its affinity is controlled by guest (irq <---> vCPU <----> pCPU),
it has no effect when host changes its affinity.

Thanks,
Feng

> 
> >
> >  	/*
> >  	 * After this point, all the interrupts will start arriving
> 
> 
> Best regards,
> Yang
> 

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