Re: [PATCH] of/device: add blacklist for iommu dma_ops
From: Robin Murphy
Date: Mon Dec 03 2018 - 07:45:54 EST
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 :/
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?
Robin.
+
arch_setup_dma_ops(dev, dma_addr, size, iommu, coherent);
return 0;