linux-kernel - Re: [PATCH v1 2/3] iommu/arm-smmu-v3-sva: Remove bond refcount

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Message-ID: <ZPchUhnSFjVpkKCe@nvidia.com>
Date:   Tue, 5 Sep 2023 09:38:42 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Michael Shavit <mshavit@...gle.com>
Cc:     iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, will@...nel.org,
        robin.murphy@....com, nicolinc@...dia.com,
        jean-philippe@...aro.org, tina.zhang@...el.com,
        Joerg Roedel <joro@...tes.org>,
        Kevin Tian <kevin.tian@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Tomas Krcka <krckatom@...zon.de>,
        Yicong Yang <yangyicong@...ilicon.com>
Subject: Re: [PATCH v1 2/3] iommu/arm-smmu-v3-sva: Remove bond refcount

On Tue, Sep 05, 2023 at 07:49:13PM +0800, Michael Shavit wrote:
> Always allocate a new arm_smmu_bond in __arm_smmu_sva_bind and remove
> the bond refcount since arm_smmu_bond can never be shared across calls
> to __arm_smmu_sva_bind.
> 
> The iommu framework will not allocate multiple SVA domains for the same
> (device/mm) pair, nor will it call set_dev_pasid for a device if a
> domain is already attached on the given pasid. There's also a one-to-one
> mapping between MM and PASID. __arm_smmu_sva_bind is therefore never
> called with the same (device/mm) pair, and so there's no reason to try
> and normalize allocations of the arm_smmu_bond struct for a (device/mm)
> pair across set_dev_pasid.
> 
> Signed-off-by: Michael Shavit <mshavit@...gle.com>
> ---
> Note that this is true today because iommu_sva_bind_device calls
> iommu_get_domain_for_dev_pasid to elude the iommu_attach_device_pasid if
> a domain is already attached.
> But even with Tina's patch series where iommu_get_domain_for_dev_pasid
> is no longer used, iommu_attach_device_pasid also checks whether a
> domain is already attached in the group's pasid_array.
> 
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 12 +-----------
>  1 file changed, 1 insertion(+), 11 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason