linux-kernel - Re: [v7 4/8] iommu, x86: No need to migrating irq for VT-d Posted-Interrupts

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Date:	Mon, 25 May 2015 10:38:21 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Feng Wu <feng.wu@...el.com>
cc:	joro@...tes.org, dwmw2@...radead.org, jiang.liu@...ux.intel.com,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [v7 4/8] iommu, x86: No need to migrating irq for VT-d
 Posted-Interrupts

On Mon, 25 May 2015, Feng Wu wrote:

> 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>
> Acked-by: David Woodhouse <David.Woodhouse@...el.com>
> ---
>  drivers/iommu/intel_irq_remapping.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
> index 1955b09..646f4cf 100644
> --- a/drivers/iommu/intel_irq_remapping.c
> +++ b/drivers/iommu/intel_irq_remapping.c
> @@ -994,7 +994,10 @@ 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->pst != 1)
> +		modify_irte(&ir_data->irq_2_iommu, irte);

I don't think this is correct. ir_data->irte_entry contains the non
posted version, which has pst == 0.

You need some other way to store whether you are in posted mode or
not.

Thanks,

	tglx
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