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

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Message-ID: <A9667DDFB95DB7438FA9D7D576C3D87E0AC0486D@SHSMSX104.ccr.corp.intel.com>
Date:	Thu, 18 Dec 2014 14:26:24 +0000
From:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
To:	"Wu, Feng" <feng.wu@...el.com>,
	"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>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"joro@...tes.org" <joro@...tes.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>
CC:	"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 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@...el.com>
> Reviewed-by: Jiang Liu <jiang.liu@...ux.intel.com>
> ---
>  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?

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


Best regards,
Yang


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