linux-kernel - Re: [PATCH v1 0/3] Clean-up arm-smmu-v3-sva.c: remove arm_smmu

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Date:   Tue, 5 Sep 2023 09:35:28 -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 0/3] Clean-up arm-smmu-v3-sva.c: remove arm_smmu_bond

On Tue, Sep 05, 2023 at 07:49:11PM +0800, Michael Shavit wrote:
> 
> This small series was originally part of a larger effort to support
> set_dev_pasid in arm-smmu-v3.c and a related SVA refactoring. But it can
> also stand on its own as an initial and prepatory clean-up.
> 
> The crux of this series relies on the observation that SVA won't
> allocate multiple SVA domains for the same device and mm pair. 

Yes, I think that is true, certainly no-intree user of this stuff
wants to do that.

It is enforced to be true after Tina's series:

https://lore.kernel.org/r/20230905000930.24515-1-tina.zhang@intel.com

Which makes one SVA domain per mm.

> There's therefore no reason for the driver to try to normalize data
> allocated for a device/mm pair across set_dev_pasid calls. 

Indeed, this is where we are trying to get to. This de-duplication
code in every driver is quite horrible.

> Note that arm-smmu-v3-sva performs a second level of normalization by
> mapping multiple bonds (now SVA domains) attached to devices with the
> same SMMU (if those devices have the same RID domain attached) to a
> single arm_smmu_mmu_notifier. This is not affected by these patches.

Ultimately the notifier should be per-iommu_domain as well.

Thanks,
Jason