Re: [PATCH rc v2] iommu/arm-smmu-v3: Do not use GFP_KERNEL under as spinlock

From: Jason Gunthorpe <jgg@nvidia.com>
To: Michael Shavit <mshavit@google.com>
Cc: Will Deacon <will@kernel.org>,
	iommu@lists.linux.dev, Joerg Roedel <joro@8bytes.org>,
	linux-arm-kernel@lists.infradead.org,
	Robin Murphy <robin.murphy@arm.com>,
	Dan Carpenter <dan.carpenter@linaro.org>,
	Nicolin Chen <nicolinc@nvidia.com>,
	patches@lists.linux.dev
Subject: Re: [PATCH rc v2] iommu/arm-smmu-v3: Do not use GFP_KERNEL under as spinlock
Date: Sat, 17 Feb 2024 09:24:46 -0400	[thread overview]
Message-ID: <20240217132446.GJ13330@nvidia.com> (raw)
In-Reply-To: <CAKHBV27eBnCrnXeaoqONWksh89tfX1b0=yvLfTkxviU_wKG_mw@mail.gmail.com>

On Sat, Feb 17, 2024 at 08:25:36PM +0800, Michael Shavit wrote:

> Calling arm_smmu_write_ctx_desc requires the CD which we get from the
> mmu_notifiers list...which makes it a bit more complicated than
> that.

@@ -404,9 +384,15 @@ static int __arm_smmu_sva_bind(struct device *dev, struct mm_struct *mm)
                goto err_free_bond;
        }
 
+       ret = arm_smmu_write_ctx_desc(master, pasid, bond->smmu_mn->cd);
+       if (ret)
+               goto err_put_notifier;
+


> > Also Michael should look at it (I recall we talked about this once)
> > and Nicolin should test it.
> 
> Just to make sure I follow why we're pursuing this instead of the v1
> rc patch: in the non-PCI multidevice group scenario, the first call to
> set_dev_pasid would only have pre-allocated for the current master but
> arm_smmu_mmu_notifier_get would then still write
> arm_smmu_write_ctx_desc to other masters?

Yes, though noting I have no idea if non-PCI exist but it does make
the code clearer and removes even the possibility of a non-atomic
allocation

Jason

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