linux-kernel - Re: [PATCH v2 4/4] iommu/arm: Add BBM Level 2 smmu feature

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Message-ID: <20250304142634.GC5011@ziepe.ca>
Date: Tue, 4 Mar 2025 10:26:34 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mikołaj Lenczewski <miko.lenczewski@....com>
Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>,
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Subject: Re: [PATCH v2 4/4] iommu/arm: Add BBM Level 2 smmu feature

On Mon, Mar 03, 2025 at 07:03:42PM +0000, Mikołaj Lenczewski wrote:

> For example, if we use BBML2 for kernel mappings, does that require us
> to repaint all kernel mappings when disabling BBML2 on smmu attach? I
> am not sure, but definitely something to be worked out.

No, it would be a per-mm_struct basis only if we did something like
that

When the SMMU driver puts a SVA on top of the mm_struct it would
disable BBML2 usage only for that mm_struct and it's contained VMAs.

Kernel mappings are never made into a SVA so are not effected.
Userspace only.

Jason