linux-kernel - Re: [PATCH 1/4] iommu/amd: Introduce Protection-domain flag VFIO

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Date:   Fri, 20 Jan 2023 13:50:25 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     "Kalra, Ashish" <ashish.kalra@....com>
Cc:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
        joro@...tes.org, robin.murphy@....com, thomas.lendacky@....com,
        vasant.hegde@....com, jon.grimm@....com
Subject: Re: [PATCH 1/4] iommu/amd: Introduce Protection-domain flag VFIO

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