Re: [PATCH v6 17/25] iommu/arm-smmu-v3: Implement iommu_sva_bind/unbind()

From: Christoph Hellwig <hch@infradead.org>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: devicetree@vger.kernel.org, kevin.tian@intel.com,
	will@kernel.org, fenghua.yu@intel.com, jgg@ziepe.ca,
	linux-pci@vger.kernel.org, felix.kuehling@amd.com,
	hch@infradead.org, linux-mm@kvack.org,
	iommu@lists.linux-foundation.org, catalin.marinas@arm.com,
	zhangfei.gao@linaro.org, robin.murphy@arm.com,
	christian.koenig@amd.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 17/25] iommu/arm-smmu-v3: Implement iommu_sva_bind/unbind()
Date: Fri, 1 May 2020 05:15:52 -0700	[thread overview]
Message-ID: <20200501121552.GA6012@infradead.org> (raw)
In-Reply-To: <20200430143424.2787566-18-jean-philippe@linaro.org>

> @@ -432,6 +432,7 @@ config ARM_SMMU_V3
>  	tristate "ARM Ltd. System MMU Version 3 (SMMUv3) Support"
>  	depends on ARM64
>  	select IOMMU_API
> +	select IOMMU_SVA
>  	select IOMMU_IO_PGTABLE_LPAE
>  	select GENERIC_MSI_IRQ_DOMAIN

Doesn't this need to select MMU_NOTIFIER now?

> +	struct mmu_notifier_ops		mn_ops;

Note: not a pointer.

> +	/* If bind() was already called for this (dev, mm) pair, reuse it. */
> +	list_for_each_entry(bond, &master->bonds, list) {
> +		if (bond->mm == mm) {
> +			refcount_inc(&bond->refs);
> +			return &bond->sva;
> +		}
> +	}
> +
> +	mn = mmu_notifier_get(&smmu_domain->mn_ops, mm);
> +	if (IS_ERR(mn))
> +		return ERR_CAST(mn);

Which seems to be to avoid mmu_notifier_get reusing notifiers registered
by other arm_smmu_master instance right?

Either you could just use plain old mmu_notifier_register to avoid
the reuse.  Or we could enhance the mmu_notifier_get to pass a private
oaque instance ID pointer, which is checked in addition to the ops,
and you could probably kill off the bonds list and lookup.

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