linux-kernel - Re: [PATCH v2 1/2] iommu/amd: Enable swiotlb in all cases

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Date:   Thu, 7 Apr 2022 06:41:09 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Mario Limonciello <mario.limonciello@....com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Suthikulpanit Suravee <Suravee.Suthikulpanit@....com>,
        Hegde Vasant <Vasant.Hegde@....com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] iommu/amd: Enable swiotlb in all cases

On Thu, Apr 07, 2022 at 02:31:44PM +0100, Robin Murphy wrote:
> FWIW it's also broken for another niche case where
> iommu_default_passthrough() == false at init, but the user later changes a
> 32-bit device's default domain type to passthrough via sysfs, such that it
> starts needing regular dma-direct bouncing.

Yeah.

We also have yet another issue:  swiotlb is not allocate if there is
no memory outside the 4GB physical address space.  I think I can fix
that easily after my swiotlb init series goes in, before that it
would be a bit of a mess spread over all the architectures.