Re: [PATCH] of/device: add blacklist for iommu dma_ops

[Rob Clark <robdclark@gmail.com>]

On Sun, Jun 2, 2019 at 11:25 PM Tomasz Figa <tfiga@chromium.org> wrote:
>
> On Mon, Jun 3, 2019 at 4:40 AM Rob Clark <robdclark@gmail.com> wrote:
> >
> > On Fri, May 10, 2019 at 7:35 AM Rob Clark <robdclark@gmail.com> wrote:
> > >
> > > On Tue, Dec 4, 2018 at 2:29 PM Rob Herring <robh+dt@kernel.org> wrote:
> > > >
> > > > On Sat, Dec 1, 2018 at 10:54 AM Rob Clark <robdclark@gmail.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@chromium.org>
> > > > > Signed-off-by: Rob Clark <robdclark@gmail.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.
>
> 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.

BR,
-R

> Best regards,
> Tomasz
>
> >
> > BR,
> > -R
> >
> > >
> > > The reason is that in the current state the core code creates the
> > > first domain before the driver has a chance to intervene and tell it
> > > not to.  And this results that driver ends up using a different
> > > context bank on the iommu than what the firmware expects.
> > >
> > > I guess the alternative is to put some property in DT.. but that
> > > doesn't really feel right.  I guess there aren't really many (or any?)
> > > other drivers that have this specific problem, so I don't really
> > > expect it to be a scaling problem.
> > >
> > > Yeah, it's a bit ugly, but I'll take a small ugly working hack, over
> > > elegant but non-working any day ;-)... but if someone has a better
> > > idea then I'm all ears.
> > >
> > > BR,
> > > -R