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

From: Jason Gunthorpe <jgg@nvidia.com>
To: Michael Shavit <mshavit@google.com>
Cc: iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, will@kernel.org,
	robin.murphy@arm.com, nicolinc@nvidia.com,
	jean-philippe@linaro.org, tina.zhang@intel.com,
	Joerg Roedel <joro@8bytes.org>, Kevin Tian <kevin.tian@intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Mark Brown <broonie@kernel.org>, Tomas Krcka <krckatom@amazon.de>,
	Yicong Yang <yangyicong@hisilicon.com>
Subject: Re: [PATCH v1 0/3] Clean-up arm-smmu-v3-sva.c: remove arm_smmu_bond
Date: Tue, 5 Sep 2023 10:32:58 -0300	[thread overview]
Message-ID: <ZPcuCo7mapUN0kt5@nvidia.com> (raw)
In-Reply-To: <CAKHBV27wi53xtDK4JzM6xH0OB7Ps0A8SewN3A0OJdpTuT2856w@mail.gmail.com>

On Tue, Sep 05, 2023 at 09:24:22PM +0800, Michael Shavit wrote:
> On Tue, Sep 5, 2023 at 8:35 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
> >
> > On Tue, Sep 05, 2023 at 07:49:11PM +0800, Michael Shavit wrote:
> > >
> > > 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.
> 
> Speaking of, I'm questioning whether the multi-SMMU domain patchseries
> and Tina's sva domain sharing are really prerequisites to get rid of
> the notifier sharing. Is anyone really depending on or taking
> advantage of this?

Currently I don't see any in-tree user of SVA on ARM except for uacce,
which seems to work with only one device (HiSillicon QM).

So, yes, you can probably make it slightly less efficient for a
time. It will be functionally correct still with multiple registered
notifiers.

Jason