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

From: Rob Clark
Date: Mon Dec 03 2018 - 09:26:44 EST

On Mon, Dec 3, 2018 at 7:45 AM Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
> Hi Rob,
>
> On 01/12/2018 16:53, Rob Clark 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.
>
> Does this crash still happen with 4.20-rc? Because as of 6af588fed391 it
> really shouldn't.
>
> > 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.
>
> s/solved/worked around/
>
> If you want a guarantee of actually getting a specific hardware context
> allocated for a given domain, there needs to be code in the IOMMU driver
> to understand and honour that. Implicitly depending on whatever happens
> to fall out of current driver behaviour on current systems is not a real
> solution.
>
> > Fixes: 97890ba9289c dma-mapping: detect and configure IOMMU in of_dma_configure
>
> That's rather misleading, since the crash described above depends on at
> least two other major changes which came long after that commit.
>
> It's not that I don't understand exactly what you want here - just that
> this commit message isn't a coherent justification for that ;)
>
> > Tested-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> > Signed-off-by: Rob Clark <robdclark@xxxxxxxxx>
> > ---
> > 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" },
> > + {}
> > +};
> > +
> > /**
> > * of_dma_configure - Setup DMA configuration
> > * @dev: Device to apply DMA configuration
> > @@ -164,6 +172,20 @@ int of_dma_configure(struct device *dev, struct device_node *np, bool force_dma)
> > dev_dbg(dev, "device is%sbehind an iommu\n",
> > iommu ? " " : " not ");
> >
> > + /*
> > + * There is at least one case where the driver wants to directly
> > + * manage the IOMMU, but if we end up with iommu dma_ops, that
> > + * interferes with the drivers ability to use dma_map_sg() for
> > + * cache operations. Since we don't currently have a better
> > + * solution, and this code runs before the driver is probed and
> > + * has a chance to intervene, use a simple blacklist to avoid
> > + * ending up with iommu dma_ops:
> > + */
> > + if (of_match_device(iommu_blacklist, dev)) {
> > + dev_dbg(dev, "skipping iommu hookup\n");
> > + iommu = NULL;
> > + }
>
> Given that a default domain will already have been allocated by the time
> we get here, regardless of whether we pretend of_iommu_configure() did
> nothing, I'm puzzled as to how this change is 'solving' that aspect as
> claimed :/

Possibly I'm reading this wrong.. I thought it is not created until
arm_iommu_create_mapping()..

but hmm, I guess I was looking at the armv7 code. Seems to be
different on arm64.. ugg..

> Is CONFIG_IOMMU_DEFAULT_PASSTHROUGH a sufficient workaround for msm at
> the moment, or do you have other devices which do actually want
> iommu_dma_ops?

I think there are at least a few other devices (venus, camera, maybe
some others that are not wired up yet?)

BR,
-R

>
> Robin.
>
> > +
> > arch_setup_dma_ops(dev, dma_addr, size, iommu, coherent);
> >
> > return 0;
> >