Date:   Mon, 3 Jun 2019 12:14:27 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Rob Clark <robdclark@...il.com>, Tomasz Figa <tfiga@...omium.org>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Christoph Hellwig <hch@....de>,
        Will Deacon <will.deacon@....com>,
        David Airlie <airlied@...ux.ie>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Sean Paul <seanpaul@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of/device: add blacklist for iommu dma_ops

On 03/06/2019 11:47, Rob Clark wrote:
> On Sun, Jun 2, 2019 at 11:25 PM Tomasz Figa <tfiga@...omium.org> wrote:
>>
>> On Mon, Jun 3, 2019 at 4:40 AM Rob Clark <robdclark@...il.com> wrote:
>>>
>>> On Fri, May 10, 2019 at 7:35 AM Rob Clark <robdclark@...il.com> wrote:
>>>>
>>>> On Tue, Dec 4, 2018 at 2:29 PM Rob Herring <robh+dt@...nel.org> wrote:
>>>>>
>>>>> On Sat, Dec 1, 2018 at 10:54 AM Rob Clark <robdclark@...il.com> wrote:
>>>>>>
>>>>>> This solves a problem we see with drm/msm, caused by getting
>>>>>> iommu_dma_ops while we attach our own domain and manage it directly at
>>>>>> the iommu API level:
>>>>>>
>>>>>>    [0000000000000038] user address but active_mm is swapper
>>>>>>    Internal error: Oops: 96000005 [#1] PREEMPT SMP
>>>>>>    Modules linked in:
>>>>>>    CPU: 7 PID: 70 Comm: kworker/7:1 Tainted: G        W         4.19.3 #90
>>>>>>    Hardware name: xxx (DT)
>>>>>>    Workqueue: events deferred_probe_work_func
>>>>>>    pstate: 80c00009 (Nzcv daif +PAN +UAO)
>>>>>>    pc : iommu_dma_map_sg+0x7c/0x2c8
>>>>>>    lr : iommu_dma_map_sg+0x40/0x2c8
>>>>>>    sp : ffffff80095eb4f0
>>>>>>    x29: ffffff80095eb4f0 x28: 0000000000000000
>>>>>>    x27: ffffffc0f9431578 x26: 0000000000000000
>>>>>>    x25: 00000000ffffffff x24: 0000000000000003
>>>>>>    x23: 0000000000000001 x22: ffffffc0fa9ac010
>>>>>>    x21: 0000000000000000 x20: ffffffc0fab40980
>>>>>>    x19: ffffffc0fab40980 x18: 0000000000000003
>>>>>>    x17: 00000000000001c4 x16: 0000000000000007
>>>>>>    x15: 000000000000000e x14: ffffffffffffffff
>>>>>>    x13: ffff000000000000 x12: 0000000000000028
>>>>>>    x11: 0101010101010101 x10: 7f7f7f7f7f7f7f7f
>>>>>>    x9 : 0000000000000000 x8 : ffffffc0fab409a0
>>>>>>    x7 : 0000000000000000 x6 : 0000000000000002
>>>>>>    x5 : 0000000100000000 x4 : 0000000000000000
>>>>>>    x3 : 0000000000000001 x2 : 0000000000000002
>>>>>>    x1 : ffffffc0f9431578 x0 : 0000000000000000
>>>>>>    Process kworker/7:1 (pid: 70, stack limit = 0x0000000017d08ffb)
>>>>>>    Call trace:
>>>>>>     iommu_dma_map_sg+0x7c/0x2c8
>>>>>>     __iommu_map_sg_attrs+0x70/0x84
>>>>>>     get_pages+0x170/0x1e8
>>>>>>     msm_gem_get_iova+0x8c/0x128
>>>>>>     _msm_gem_kernel_new+0x6c/0xc8
>>>>>>     msm_gem_kernel_new+0x4c/0x58
>>>>>>     dsi_tx_buf_alloc_6g+0x4c/0x8c
>>>>>>     msm_dsi_host_modeset_init+0xc8/0x108
>>>>>>     msm_dsi_modeset_init+0x54/0x18c
>>>>>>     _dpu_kms_drm_obj_init+0x430/0x474
>>>>>>     dpu_kms_hw_init+0x5f8/0x6b4
>>>>>>     msm_drm_bind+0x360/0x6c8
>>>>>>     try_to_bring_up_master.part.7+0x28/0x70
>>>>>>     component_master_add_with_match+0xe8/0x124
>>>>>>     msm_pdev_probe+0x294/0x2b4
>>>>>>     platform_drv_probe+0x58/0xa4
>>>>>>     really_probe+0x150/0x294
>>>>>>     driver_probe_device+0xac/0xe8
>>>>>>     __device_attach_driver+0xa4/0xb4
>>>>>>     bus_for_each_drv+0x98/0xc8
>>>>>>     __device_attach+0xac/0x12c
>>>>>>     device_initial_probe+0x24/0x30
>>>>>>     bus_probe_device+0x38/0x98
>>>>>>     deferred_probe_work_func+0x78/0xa4
>>>>>>     process_one_work+0x24c/0x3dc
>>>>>>     worker_thread+0x280/0x360
>>>>>>     kthread+0x134/0x13c
>>>>>>     ret_from_fork+0x10/0x18
>>>>>>    Code: d2800004 91000725 6b17039f 5400048a (f9401f40)
>>>>>>    ---[ end trace f22dda57f3648e2c ]---
>>>>>>    Kernel panic - not syncing: Fatal exception
>>>>>>    SMP: stopping secondary CPUs
>>>>>>    Kernel Offset: disabled
>>>>>>    CPU features: 0x0,22802a18
>>>>>>    Memory Limit: none
>>>>>>
>>>>>> The problem is that when drm/msm does it's own iommu_attach_device(),
>>>>>> now the domain returned by iommu_get_domain_for_dev() is drm/msm's
>>>>>> domain, and it doesn't have domain->iova_cookie.
>>>>>>
>>>>>> We kind of avoided this problem prior to sdm845/dpu because the iommu
>>>>>> was attached to the mdp node in dt, which is a child of the toplevel
>>>>>> mdss node (which corresponds to the dev passed in dma_map_sg()).  But
>>>>>> with sdm845, now the iommu is attached at the mdss level so we hit the
>>>>>> iommu_dma_ops in dma_map_sg().
>>>>>>
>>>>>> But auto allocating/attaching a domain before the driver is probed was
>>>>>> already a blocking problem for enabling per-context pagetables for the
>>>>>> GPU.  This problem is also now solved with this patch.
>>>>>>
>>>>>> Fixes: 97890ba9289c dma-mapping: detect and configure IOMMU in of_dma_configure
>>>>>> Tested-by: Douglas Anderson <dianders@...omium.org>
>>>>>> Signed-off-by: Rob Clark <robdclark@...il.com>
>>>>>> ---
>>>>>> This is an alternative/replacement for [1].  What it lacks in elegance
>>>>>> it makes up for in practicality ;-)
>>>>>>
>>>>>> [1] https://patchwork.freedesktop.org/patch/264930/
>>>>>>
>>>>>>   drivers/of/device.c | 22 ++++++++++++++++++++++
>>>>>>   1 file changed, 22 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/of/device.c b/drivers/of/device.c
>>>>>> index 5957cd4fa262..15ffee00fb22 100644
>>>>>> --- a/drivers/of/device.c
>>>>>> +++ b/drivers/of/device.c
>>>>>> @@ -72,6 +72,14 @@ int of_device_add(struct platform_device *ofdev)
>>>>>>          return device_add(&ofdev->dev);
>>>>>>   }
>>>>>>
>>>>>> +static const struct of_device_id iommu_blacklist[] = {
>>>>>> +       { .compatible = "qcom,mdp4" },
>>>>>> +       { .compatible = "qcom,mdss" },
>>>>>> +       { .compatible = "qcom,sdm845-mdss" },
>>>>>> +       { .compatible = "qcom,adreno" },
>>>>>> +       {}
>>>>>> +};
>>>>>
>>>>> Not completely clear to whether this is still needed or not, but this
>>>>> really won't scale. Why can't the driver for these devices override
>>>>> whatever has been setup by default?
>>>>>
>>>>
>>>> fwiw, at the moment it is not needed, but it will become needed again
>>>> to implement per-context pagetables (although I suppose for this we
>>>> only need to blacklist qcom,adreno and not also the display nodes).
>>>
>>> So, another case I've come across, on the display side.. I'm working
>>> on handling the case where bootloader enables display (and takes iommu
>>> out of reset).. as soon as DMA domain gets attached we get iommu
>>> faults, because bootloader has already configured display for scanout.
>>> Unfortunately this all happens before actual driver is probed and has
>>> a chance to intervene.
>>>
>>> It's rather unfortunate that we tried to be clever rather than just
>>> making drivers call some function to opt-in to the hookup of dma iommu
>>> ops :-(
>>
>> I think it still works for the 90% of cases and if 10% needs some
>> explicit work in the drivers, that's better than requiring 100% of the
>> drivers to do things manually.

Right, it's not about "being clever", it's about not adding opt-in code 
to the hundreds and hundreds and hundreds of drivers which *might* ever 
find themselves used on a system where they would need the IOMMU's help 
for DMA.

>> Adding Marek who had the same problem on Exynos.
> 
> I do wonder how many drivers need to iommu_map in their ->probe()?
> I'm thinking moving the auto-hookup to after a successful probe(),
> with some function a driver could call if they need mapping in probe,
> might be a way to eventually get rid of the blacklist.  But I've no
> idea how to find the subset of drivers that would be broken without a
> dma_setup_iommu_stuff() call in their probe.

Wouldn't help much. That particular issue is nothing to do with DMA ops 
really, it's about IOMMU initialisation. On something like SMMUv3 there 
is literally no way to turn the thing on without blocking unknown 
traffic - it *has* to have stream table entries programmed before it can 
even allow stuff to bypass.

The answer is either to either pay attention to the "Quiesce all DMA 
capable devices" part of the boot protocol (which has been there since 
pretty much forever), or to come up with some robust way of 
communicating "live" boot-time mappings to IOMMU drivers so that they 
can program themselves appropriately during probe.

Robin.

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