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Date:   Tue, 6 Jul 2021 06:48:48 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Will Deacon <will@kernel.org>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Claire Chang <tientzu@chromium.org>,
        Rob Herring <robh+dt@kernel.org>, mpe@ellerman.id.au,
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        Christoph Hellwig <hch@lst.de>,
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        "list@263.net:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
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Subject: Re: [PATCH v15 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing
Message-ID: <20210706044848.GA13640@lst.de>
References: <YNvMDFWKXSm4LRfZ@Ryzen-9-3900X.localdomain> <CALiNf2-a-haQN0-4+gX8+wa++52-0CnO2O4BEkxrQCxoTa_47w@mail.gmail.com> <20210630114348.GA8383@willie-the-truck> <YNyUQwiagNeZ9YeJ@Ryzen-9-3900X.localdomain> <20210701074045.GA9436@willie-the-truck> <ea28db1f-846e-4f0a-4f13-beb67e66bbca@kernel.org> <20210702135856.GB11132@willie-the-truck> <0f7bd903-e309-94a0-21d7-f0e8e9546018@arm.com> <YN/7xcxt/XGAKceZ@Ryzen-9-3900X.localdomain> <20210705190352.GA19461@willie-the-truck>
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On Mon, Jul 05, 2021 at 08:03:52PM +0100, Will Deacon wrote:
> So at this point, the AMD IOMMU driver does:
> 
> 	swiotlb        = (iommu_default_passthrough() || sme_me_mask) ? 1 : 0;
> 
> where 'swiotlb' is a global variable indicating whether or not swiotlb
> is in use. It's picked up a bit later on by pci_swiotlb_late_init(), which
> will call swiotlb_exit() if 'swiotlb' is false.
> 
> Now, that used to work fine, because swiotlb_exit() clears
> 'io_tlb_default_mem' to NULL, but now with the restricted DMA changes, I
> think that all the devices which have successfully probed beforehand will
> have stale pointers to the freed structure in their 'dev->dma_io_tlb_mem'
> field.

Yeah.  I don't think we can do that anymore, and I also think it is
a bad idea to start with.