linux-kernel - Re: [PART2 PATCH v3 07/11] iommu/amd: Introduce amd_iommu_update

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Date:	Mon, 11 Jul 2016 20:59:43 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:	joro@...tes.org, pbonzini@...hat.com, alex.williamson@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	sherry.hurwitz@....com
Subject: Re: [PART2 PATCH v3 07/11] iommu/amd: Introduce amd_iommu_update_ga()

2016-07-11 05:11-0500, Suravee Suthikulpanit:
> From: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> 
> Introduces a new IOMMU API, amd_iommu_update_ga(), which allows
> KVM (SVM) to update existing posted interrupt IOMMU IRTE when
> load/unload vcpu.
> 
> Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> ---
> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> @@ -4481,4 +4481,67 @@ int amd_iommu_create_irq_domain(struct amd_iommu *iommu)
> +int amd_iommu_update_ga(u32 vcpu_id, u32 cpu, u32 ga_tag,
> +			u64 base, bool is_run)

Not just in this function does the interface between svm and iommu split
ga_tag into its two components (vcpu_id and ga_tag), but it seems that
the combined value could always be used instead ...
Is there an advantage to passing two values?

> +{
> +	unsigned long flags;
> +	struct amd_iommu *iommu;
> +
> +	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))
> +		return 0;
> +
> +	for_each_iommu(iommu) {
> +		struct amd_ir_data *ir_data;
> +
> +		spin_lock_irqsave(&iommu->ga_hash_lock, flags);
> +
> +		/* Note: Update all possible ir_data for a particular
> +		 * vcpu in a particular vm.
> +		 */
> +		hash_for_each_possible(iommu->ga_hash, ir_data, hnode,
> +				       AMD_IOMMU_GATAG(ga_tag, vcpu_id)) {
> +			struct irte_ga *irte = (struct irte_ga *) ir_data->entry;

(The ga_tag check is missing here too.)

> +			if (!irte->lo.fields_vapic.guest_mode)
> +				continue;
> +
> +			update_irte_ga((struct irte_ga *)ir_data->ref,
> +					ir_data->irq_2_irte.devid,
> +					base, cpu, is_run);

(The lookup leading up to here is avoidable -- svm, the caller, has the
 ability to map ga_tag into irte/ir_data directly with a pointer.
 I'm not sure if the lookup is slow enough to pardon optimization, but
 it might make the code simpler as well.)

> +			iommu_flush_irt(iommu, ir_data->irq_2_irte.devid);
> +			iommu_completion_wait(iommu);
> +		}
> +
> +		spin_unlock_irqrestore(&iommu->ga_hash_lock, flags);