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Date:   Fri, 20 Jan 2023 13:50:25 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     "Kalra, Ashish" <ashish.kalra@amd.com>
Cc:     Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
        joro@8bytes.org, robin.murphy@arm.com, thomas.lendacky@amd.com,
        vasant.hegde@amd.com, jon.grimm@amd.com
Subject: Re: [PATCH 1/4] iommu/amd: Introduce Protection-domain flag VFIO
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On Fri, Jan 20, 2023 at 11:01:21AM -0600, Kalra, Ashish wrote:

> We basically get the RMP #PF from the IOMMU because there is a page size
> mismatch between the RMP table and the IOMMU page table. The RMP table's
> large page entry has been smashed to 4K PTEs to handle page state change to
> shared on 4K mappings, so this change has to be synced up with the IOMMU
> page table, otherwise there is now a page size mismatch between RMP table
> and IOMMU page table which causes the RMP #PF.

I understand that, you haven't answered my question:

Why is the IOMMU being programmed with pages it cannot access in the
first place?

Don't do that is the obvious solution there, and preserves huge page
IO performance.

Jason