linux-kernel - Re: [PATCH v15 06/12] swiotlb: Use is_swiotlb_force

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Message-ID: <20210705190352.GA19461@willie-the-truck>
Date:   Mon, 5 Jul 2021 20:03:52 +0100
From:   Will Deacon <will@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Claire Chang <tientzu@...omium.org>,
        Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        Joerg Roedel <joro@...tes.org>,
        Frank Rowand <frowand.list@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        benh@...nel.crashing.org, paulus@...ba.org,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        grant.likely@....com, xypron.glpk@....de,
        Thierry Reding <treding@...dia.com>, mingo@...nel.org,
        bauerman@...ux.ibm.com, peterz@...radead.org,
        Greg KH <gregkh@...uxfoundation.org>,
        Saravana Kannan <saravanak@...gle.com>,
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        heikki.krogerus@...ux.intel.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-devicetree <devicetree@...r.kernel.org>,
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        Bjorn Helgaas <bhelgaas@...gle.com>, chris@...is-wilson.co.uk,
        Daniel Vetter <daniel@...ll.ch>, airlied@...ux.ie,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        jani.nikula@...ux.intel.com, Jianxiong Gao <jxgao@...gle.com>,
        joonas.lahtinen@...ux.intel.com, linux-pci@...r.kernel.org,
        maarten.lankhorst@...ux.intel.com, matthew.auld@...el.com,
        rodrigo.vivi@...el.com, thomas.hellstrom@...ux.intel.com,
        Tom Lendacky <thomas.lendacky@....com>,
        Qian Cai <quic_qiancai@...cinc.com>
Subject: Re: [PATCH v15 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing

Hi Nathan,

I may have just spotted something in these logs...

On Fri, Jul 02, 2021 at 10:55:17PM -0700, Nathan Chancellor wrote:
> [    2.340956] pci 0000:0c:00.1: Adding to iommu group 4
> [    2.340996] pci 0000:0c:00.2: Adding to iommu group 4
> [    2.341038] pci 0000:0c:00.3: Adding to iommu group 4
> [    2.341078] pci 0000:0c:00.4: Adding to iommu group 4
> [    2.341122] pci 0000:0c:00.6: Adding to iommu group 4
> [    2.341163] pci 0000:0d:00.0: Adding to iommu group 4
> [    2.341203] pci 0000:0d:00.1: Adding to iommu group 4
> [    2.361821] pci 0000:00:00.2: AMD-Vi: Found IOMMU cap 0x40
> [    2.361839] pci 0000:00:00.2: AMD-Vi: Extended features (0x206d73ef22254ade):
> [    2.361846]  PPR X2APIC NX GT IA GA PC GA_vAPIC
> [    2.361861] AMD-Vi: Interrupt remapping enabled
> [    2.361865] AMD-Vi: Virtual APIC enabled
> [    2.361870] AMD-Vi: X2APIC enabled
> [    2.362272] AMD-Vi: Lazy IO/TLB flushing enabled

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.

Will